Jonas Quinn was sort of like Daniel Jackson... but from another planet! However, after Michael Shanks decided to return as a regular, Jonas Quinn was abruptly and permanently written out of the series at the beginning of the seventh season.
Despite being the Trope Namer for a while, Jonas Quinn wasn't even the best example of this trope on this show. Cam Mitchell, an Air Force colonel with a snarky sense of humor and a tendency to make pop culture references (like the actor Browder's character in Farscape) replaced Richard Dean Anderson's character, Jack O'Neill, when he started Commuting on a Bus to spend more time with his family. This somewhat falls under the "military role" exception, but is more likely due to a desire to have a new leading man, particularly one with a built-in audience. In addition, the "military role" exception doesn't explain their sufficiently similar personalities; Mitchell hadn't Seen It All like O'Neill, had a lower rank and lacks the Ancient gene, but other than that they could have delivered the same lines.
This trope received its Lampshade Hanging (along with about a hundred others) in "200," when an actor backs out from playing the lead in the Show Within a Show based on the SG team's adventures, leading to the page quote above. And at the end, we find out the "Colonel Danning" character from Wormhole X-Treme! was substituted. "Dr. Levant" is not indicated to have had a Suspiciously Similar Substitute when he left the show, but much like the realStargate SG-1, they may have resolved to never speak of it.
Not to mention the humorous scene where other characters suggested that Cam was O'Neill's son from the time travel episode in Season 1.
Jewel Staite's Dr. Keller also replaced Dr. Beckett on Stargate Atlantis as the caring and sometimes out of his/her element doctor, despite having appeared on the series previously as a different character.
Supernatural has Balthazar, who's very, very similar to the now-dead Gabriel (except taller, blonder, and with a hot British accent).
Later in the series, fans commented that the character "Frank" was just an unnecessary replacement for Bobby, who was taken away from the leads to supposedly "strip the show back down to just the brothers."
Arguably, this fate has now befallen the character "Kevin" (with a dose of flanderization to boot), who, since the Men of Letters bunker was introduced, is little more than a walking-talking Junior Woodchucks Guidebook.
When he was first introduced, many fans feared that Benny would replace Castiel as Dean's gravel-voiced, coat-wearing, non-human BFF.
On Cheers, the sweet-natured, dimwitted old bartender Coach was replaced by the sweet-natured, dimwitted young bartender Woody Boyd. Rebecca Howe (a ruthless and hot corporate exec) was more distinct from her predecessor Diane (a bookish and pretty in a girl-next-door-way barmaid), but Rebecca gradually became more and more like Diane.
Al, the elderly man who sat at the opposite corner of the bar from Norm and occasionally made sarcastic comments, was replaced by Phil, the elderly man who sat at the opposite corner of the bar from Norm and occasionally made sarcastic comments. In the Reunion Show episode of Frasier, Frasier says how good it is to see Al again, only to be told "I'm Phil, you jackass! Al died!"
Speaking of Frasier, this trope was neatly deconstructed/lampshaded with Mel Karnofski, Niles' Romantic False Lead between divorcing Maris and getting together with Daphne. Mel was a blatantly obvious slightly-milder carbon-copy of Maris (or rather, Maris's actions and descriptions given a more subtle form and voice), paralleling her in everything from being a manipulative and domineering Jerk Ass to her hysterical, unstable, mood-swinging, and obsessively fussy and neurotic behavior — and Niles is unable to see it. Frasier outright tells Niles that he's repeating a horrible pattern (Maris was quite emotionally abusive and generally had an adverse effect on Niles' mental state), and speculates that he's just jumping at the chance for someone comfortingly familiar because Daphne is getting engaged and he (apparently) no longer has a chance with her.
Also the various informants, starting with Deep Throat, coming into X, and finishing with Marita Covarrubias.
One case was forced: "Travelers" and "Agua Mala" featured Arthur Dales, the first FBI agent to deal with X-Files. Dales' actor Darren McGavin suffered a stroke filming "The Unnatural", leading him to be replaced with M. Emmet Walsh playing his brother Arthur Dales, a former police officer (who lampshades his parents didn't have much creativity with names). To make it worse, both Dales were played in flashbacks by the same actor.
M*A*S*H replaced half its original cast during its run with new characters slotted into their roles in the ensemble, but partially subverted the trope by giving the new characters key differences. Womanizer Trapper John was replaced by happily married B.J. Hunnicutt, oblivious draftee Col. Blake was replaced by regular-Army taskmaster Col. Potter, incompetent Jerkass Frank Burns was replaced by Jerk with a Heart of Gold surgical diva Charles Winchester. Clerical savant Radar wasn't given a replacement character but instead his duties were handed off to slacker first-class Klinger.
This is lampshaded depressingly in the episode "Depressing News", when Hawkeye is lamenting to B.J. how the war rolls on even as the people fighting it are killed or replaced (using the surplus tongue depressors that have been shipped to the 4077th as a visual aid):
Hawkeye: Tongue depressors, doctors, soldiers, we're all the same...(holds up one tongue depressor) Trapper John goes. No problem, there's plenty more where he came from. (tosses it aside and picks up another) B.J. Hunnicutt. Same size, same shape. (picks up another) Frank Burns out... (picks up another) Winchester in. Just a hair's difference. (picks up another) Henry Blake. (snaps it in two) Rest in peace, Henry. (picks up another) Incoming Sherman Potter. (to B.J.) My God, hasn't this elimination tournament gone on long enough?
Sgt. Luther Rizzo is arguably a substitute for Sgt. Zelmo Zale.
Jeffrey Sinclair and John Sheridan (both J.S.'s, like J. Michael Straczynski), and, later, Susan Ivanova and Elizabeth Lochley, on Babylon 5. The difference between the two changes and their effect on the show is marked, as was general reaction.
Ivanova was herself a Suspiciously Similar Substitute for Laurel Takashima from the Pilot MovieBabylon 5: The Gathering.
That's how it ended up, but according to JMS that wasn't the original intention. The two characters were originally supposed to coexist until the end of the second season when Laurel would turn out to be The Mole and leave the show (written in because JMS knew Tamlyn Tomita wouldn't want to commit to five years) and Ivanova would become the executive officer... but then Tamlyn Tomita decided not to come back for the series at all.
Likewise, Talia Winters replaced Lyta Alexander when the series began; in a recursive twist, though, when Andrea Thompson decided to leave the show, they brought back Lyta in a double-un-Suspiciously Similar Substitute maneuver.
Word of God admits this was a blatant Bridge Drop. Talia's actress was clamoring for more screen time and generally being a pain to work with, so JMS unceremoniously fired her. Additionally served as a standing notice to other cast that Anyone Can Die, in addition to the flexibility mentioned below.
Stephen Franklin replaced Benjamin Kyle. Noticing a pattern yet? Face it — if this wiki had been around ten years ago, the page you're reading would be called "John Sheridan."
Straczynski has stated that every major character on the show had an "escape hatch" for each season, to allow the actor to be replaced if necessary without affecting the overall story arc.
Babylon 5 did this with alien species too. After the Shadows left the galaxy, a suspiciously similar race called the Drakh appeared, handwaved as the "dark servants" of the Shadows.
Flo replacing the deceased Selma on Night Court. Flo then also died a year later, leading to the younger Roz. (Also on this show, Lana was replaced by Mac, and Liz was replaced by Billie, then Christine).
Mystery Science Theater 3000 is an interesting case. All characters other than the robots had been replaced by the show's end, yet the writers took care to make the replacement (and their interaction with the rest of the cast) different from the departing character. Consequently, there's no real consensus among the fans whether any given replacement was better or worse than the original. It also helps that each replacement actor was either behind the scenes since the start, or with the team for ages before they got in front of the camera, so none of them were really "new."
Joel was sort of a father figure to the 'bots. His replacement, Mike, interacted with the 'bots as their equal (at best) and tended to be more overtly sarcastic. The flame wars over which of the two was better are notorious. While the bots see Joel as a father figure, they see Mike as a brother figure thus are more inclined to mess around with Mike and prank him relentlessly than they would Joel.
TV's Frank was Dr. Clayton Forrester's minion and punching-bag; when he departed, he was replaced by Pearl Forrester, Clayton's mom and one of the few people capable of cowing her son into submission. After Clayton departed, Pearl took over as the head Mad, and gained her own minions, Bobo and Observer.
TV's Frank himself being a replacement for Dr Erhardt, who "went missing" after the first season. Prompting Joel to remark during "Earth vs. The Spider" when a character who looked alot like Dr Erhardt was eaten "So THATS what happened to him!"
The actor playing Dr. Erhardt also provided the voice of Tom Servo during the show's first Comedy Channel season. When he left, and Kevin took over for Tom Servo in season 2, a fan mailed in an 11-page long banner screaming "I HATE SERVO'S NEW VOICE". ("Does he realize," Kevin later commented, "That he just sent hate mail to a puppet?")
Farscape mostly averted this. After Zhaan dies, she's replaced by Jool who fills the same role as The Smart Guy but is purely scientific rather than spiritual and is much more abrasive in personality, while Stark tries to take over Zhaan's spiritual role (with mixed results.) When Jool leaves, her direct replacement Sikozu is a bit more similar in personality to her but much more competent and calculating. At the same time, Noranti is introduced as a replacement for Zhann and Stark's mystical/spiritual role, but more morally ambiguous than Zhaan was, sometimes being downright sinister. As well as replacing the missing Stark's allotment of crazy awesome.
One episode even featured a group of suspiciously similar substitutes. Escaped prisoners from Peacekeeper custody on a Leviathan transport pod, a Scarran strong guy (reflecting D'Argo's proud warrior race guy), a Nebari androgyn (hermaphrodite, mirroring Chiana's nonconformist), a female Hynerian, and a captured Peacekeeper tech (reflecting Aeryn's initial unwilling accompaniment of Moya's crew, as well as looking similar to Crichton and being in a similarly mistrusted position.)
Sergeant Baker replaced Sergeant Kinchloe as 'radio operator who happens to be black' on Hogan's Heroes in the final season. Unfortunately, unlike Kinchloe, Baker didn't have much characterization outside 'radio operator who happens to be black' and wasn't the most satisfying of replacements.
An interesting exception can be found on A Different World. Originally it was a star vehicle created for Lisa Bonet by Bill Cosby's production house, but after Bonet's 1988 pregnancy forced her from the program after the first season, no substitute for her was cast. Instead, it became an ensemble show, and eventually two minor characters — Dwayne Wayne and Whitley Gilbert — evolved into its real stars and carried the show for five more years.
They also had the character of Flash, nicknamed because he was an adult with the hyperactivity of a 4 year old. Essentially another Cody given a justification.
In Heroes, West's relationship with Claire leaves him as little more than a straight version of Zach. The writers tried to cover this up by giving him the power of flight/levitation but his lines and role as a foil character made it obvious.
Star Trek eventually fell into this trap — particularly with Star Trek: Voyager and Star Trek: Enterprise — though for different reasons. ENT was intentionally a merging of the holy trinity of Kirk, Spock and Bones with the "new generation" Trek tropes. Conversely, VOY germinated as an unaired eighth season of TNG before being retooled into a spinoff.
Actually this trope has been in Star Trek from the start, where Captain Pike is replaced after the Pilot with Captain Kirk. Both are square jawed, two fisted adventurers with a close friendship with the ship's physician and a mild romantic interest in a female yeoman.
Pike was not exactly an established character, though, since the pilot was not shown in the series' regular run. Yes, it was chopped up to become the story-within-a-story of "Menagerie" but that was run well after Kirk was established as Captain. The Abrams films later canonized Pike as a vital character in his own right. Unfortunately for Pike, his death has become a series staple, as well!
The characters of TOS were based on the characters originally conceived for the rejected pilot, with Pike becoming Kirk, Boyce becoming Bones, Smith becoming Rand, etc.. This practice is extremely commonplace when a Pilot turns into a green-lighted series. Similarly, the characters of TNG were based on the characters of the abandoned "Star Trek: Phase II" series: Will Decker became the similarly-named Will Riker; Decker's old flame, the empathic Deltan Ilia, became Riker's old flame, the empathic Betazed Troi; and Xon, the Vulcan struggling to understand humanity, became Data, the android struggling to understand humanity. A writer's strike proved to be nothing more than a minor inconvenience for TNG: they just dusted off some old "Phase II" scripts and went to work (though only one script ended up being used for the strike-shortened second season; another was pushed back to season four).
Xon was created to replace Spock when Leonard Nimoy decided he didn't want to do the "Phase II" series.
Following the success of TNG, a pattern began to emerge in the crew's makeup. There will always be an overeager, wet behind the ears kid for the young audience to relate to (see Wesley Crusher, Jake Sisko, Naomi Wildman); an inexperienced recruit (Dr. Bashir, Harry Kim, Travis Mayweather); a comic relief hustler with gross alien habits (see Quark, Neelix, and Dr. Phlox). Sometimes the characters were just obvious stand-ins for a more famous predecessor: Tuvok, the gruff, socially-awkward Vulcan security officer, was substituted for Worf, the gruff, socially awkward Klingon security officer for instance.
For one season of Star Trek: The Next Generation, Dr. Kate Pulaski (played by Diana Muldaur, who'd appeared twice as different characters in the Original Series) replaced Dr. Beverly Crusher as ship's doctor. Pulaski was doubly a Suspiciously Similar Substitute, since her abrasive tics were explicitly based on Bones McCoy.
In a case falling halfway between Suspiciously Similar Substitute and The Nth Doctor, Star Trek: Deep Space Nine replaced Jadzia Dax with Ezri Dax in the final season: different hosts, same symbiote, and a Trill's personality is a blend of the host and symbiote.
The exact same thing happened in the early production of Star Trek: Voyager: B'Elanna Torres was also a replacement character for Ro Laren, because Michelle Forbes again refused to commit to a seven-year show.
The character Tom Paris from Voyager was originally slated to be Nicolas Locarno (a single-episode character from TNG) but the producers did not want to get into a situation where they may be forced to pay royalties to the original writer of the TNG episode so they changed the name of the character. Then turned this trope Up to Eleven as both characters were played by the same actor.
Taurik, a Vulcan Ensign who appeared in a single episode of Star Trek: The Next Generation, became a recurring crew member in Voyager, where he was called Vorik, for the same reason that Locarno became Paris and T'Pau became T'Pol. Jeri Taylor, a producer on Voyager and the mother of the actor (Alexander Enberg) who played Taurik and Vorik, once quipped that the rhymedly named Vulcan Ensigns were identical twin brothers.
To complete a common pattern, T'Pol was originally written to be T'Pau, a Vulcan priestess who appeared in the Original Series. But since it was thought at the time that reusing a character would force them to pay royalties to the writer who created the original T'Pau (see Tom above), the character was changed. T'Pau did appear in the fourth season during a story arc on Vulcan. It was some years later that a judge in California ruled that such a reuse would not force a producer to pay royalties to the original writer. (This, incidentally, is one of the reasons why Nicholas Locarno in TNG became Tom Paris in Voyager).
One of the world's few substitute anticipations happened in the kids' series Space Cases. With Jewel Staite having Flash Forward hanging in the balance, her character, Catalina, was given an "imaginary friend" named Suzee, who was really a person living in Another Dimension that Catalina could communicate with. When the other series required Ms. Staite's services, a little Applied Phlebotinum switched Suzee to the real world (as played by Rebecca Herbst) and Catalina to the "imaginary" world.
Beakmans World substituted its lovely young female assistant not once, but twice. Both were a result of the show's fate: The first switch happened as the show moved to CBS from syndication (and Alanna Ubach deciding to do movies instead), and the second happened after an Un-cancellation (and Eliza Schneider deciding to do stage shows instead).
Many older kids shows, like You Cant Do That On Television and Kids Incorporated, substituted the entire cast, and Kids Incorporated did so repeatedly. Their reasoning is likely similar to why the Vienna Boys' Choir and Menudo boot their kids out at 13.
Similarly, the late 80s-early 90s incarnation of The Mickey Mouse Club turned over its cast a few times. Notables in the mix include Keri Russell (as part of the first rotation of new blood) and Britney Spears (as part of one of the last rotations).
The UK kids' show Why Dont You... is another example, but is had one notable exception in its later years: Ben, the Welsh Mad Scientist, was evidently considered un-substitutable, so he continued past the typical age, eventually playing a Holly-style computer program based on the original Ben, so that the disparity between his age and the rest of the cast wasn't an issue.
They did manage a successful change in Power Rangers Lost Galaxy, where actress Valerie Vernon had to leave due to being diagnosed with leukemia. Originally they were going to take the previous pink ranger and bring her in as a replacement, but when that deal fell through, they took the previous season's reformed Big Bad, Karone, and made her the replacement. In this case, the character was vastly different because she had aspects of The Atoner.
Another successful change was Adam Park, the second Black Ranger. While Zack was fun-loving and energetic, Adam was fairly quiet and thoughtful. Early on, this was all his character had to him, but an ad-lib in The Movie (his dejected "I'm a frog..." when finding out what his spirit animal is) gave him some Woobie points and being the second-longest serving ranger gave him fairly decent character development. He's one of the most popular characters in the series now and the only pre-Disney buyout ranger to appear in the 15th anniversary Reunion Show.
Teen Wolf has become a major offender of this trope in recent seasons, especially with its female characters. The best example is Cora, who seems to be this for Erica, the only female werewolf in Derek's pack. From being the one seen trapped in the vault with Boyd (when many wondered if Gage Golightly may have made a surprise return) to her relationship with Stiles, which is similarly part snarky and part flirtatious, she's just too similar to Erica for viewers to overlook.
And now, since Adelaide Kane (Cora) left the show, we have a Suspiciously Similar Substitute for the Suspiciously Similar Substitute with Malia Tate.
After Allison's death, Kira appears to be her substitute as Scott's love interest.
Taken Up to Eleven in Season 4, which saw the addition of Mason, a gay male high school freshman who's a POC, star athlete on the lacrosse team, best friends with blond jock Liam, and isn't aware of the supernatural events going on around him. Sounds great until you realize that that almost word for word describes Danny Mahealani, who was mysteriously cut from Season 4, has had minimal Character Development since Jackson's departure two seasons ago, and was an Ensemble Darkhorse amongst the fandom and casual viewers.
The original Kamen Rider was forced to do this with Takeshi Hongo/Kamen Rider 1 after Hiroshi Fujioka broke his leg while attempting a stunt. Unlike many examples of this trope, however, the replacement character (Hayato Ichimonji/Kamen Rider 2) is remembered fondly by the fanbase and has become just as much a fixture of the franchise as his predecessor, and when the former returned to the show, the two are often paired under the nickname "Double Riders."
Kamen Rider Decade did this to most of the cast of the shows they visited, using the conceit of Alternate Universes. However, while most of the characters got substitutes, several of the original actors gladly returned to reprise their roles (even if they were alternate universe versions). The most stand-out example is Kamen Rider Hibiki, where most of the secondary cast came back, but the actors who played the show's two stars (Hibiki and Asumu) didn't.
The old-school Riders had a recurring, cross-seasonal ally named Tobei Tachibana. He started out as Hongo's friend who ran the motorbike racing club, but got more and more involved with things Rider-related just due to being close to the guys trouble followed most, becoming something of a Badass Normal. When Powers That Be decided to bring the character back in Kamen Rider Skyrider but the actor declined, the Tachibana role in that and the following series went to the nigh-identical Genjiro Tani. His personality and role were exactly Tachibana's, and sometimes past Riders talked to Tani as if they knew him much better than they did, as if scripts with Tachibana in mind had already been written. They really shoulda gone the Magic Plastic Surgery route.
The Metal Heroes series Space Sheriff Gavan has Gavan's Bridge Bunny Mimi leave to see to her ill mother for the last 3rd or so of the series, and replaced with a character called Marin who was the exact same character minus the Love Interest part (since Mimi was only leaving for a short while so her and Gavan were still technically in a relationship). Unlike most examples, though, Marin was already an established character on the show as a Bridge Bunny to Gavan's Mission Control and was specifically called in to fill in for Mimi.
Will Bailey seems to have begun as one for Sam Seaborn (right down to several "passing the torch" incidents in which Sam encouraged Toby to accept Will's help with the Inauguration speech, Will was semi-formally inducted into Sam's old position, etc.), but the writing of the show shifted after Aaron Sorkin's departure, and within a year Will's character had shifted jobs into the Vice-President's office and was portrayed more as a cynical political operative than as an idealist. Joshua Malina (Will) has even described himself as a worse-looking, less-expensive Rob Lowe (Sam). Which you have to admit has a grain of truth to it.
Joe Quincy (Matthew Perry), who was hired to fill a position opened by Ainsley Hayes (Emily Procter), a "blonde, leggy Republican." Yeah, he was a Republican too. Josh doesn't like that the similarities end there.
Josh: If you're a Republican, you damn well better look like Ainsley Hayes! Donna: He does! [Joe and Josh stare] Donna: I mean... he will to other people!
The show seems to be unable to hang on to the actor playing the White House Counsel, and so the feeling of similarity is probably due to the fact that the dialogue the new guy is sprouting was actually written for the previous guy. The scene that introduces Counsel Oliver Babish (the one with the oversized gavel and dictaphone) was pretty obviously written with Lionel Tribbey (his predecessor) in mind.
Maverick introduced a Suspiciously Similar Substitute before the star left, in the form of Bret Maverick's brother, Bart. This was principally done in order to accelerate the show's shooting schedule, since they could shoot a Bret episode and a Bart episode at the same time. Reportedly, the show's writers had no idea whether a given episode would be a Bret episode or a Bart episode when they wrote it. By the show's end there were two other Mavericks in rotation, one of them played by Roger Moore. The most suspiciously similar of them all was Brent Maverick, who was introduced shortly after James Garner (who played Bret Maverick) left the show. Not only was Brent's name just one letter off from Bret's, but he was played by Robert Colbert, who bears a remarkable likeness to Garner. When Colbert discovered the producers' plan for him, he rebelled against them, reportedly begging them to, "Put me in a dress and call me Brenda! ANYTHING but this!"
To an extent, Hugh Laurie in the third and fourth series of Blackadder seems to have filled this role (aristocratic fop) in replacement of Tim McInnerny from the first two series, after McInnerny left because he didn't want to be typecast. When McInnerny rejoined the regular cast in the fourth series, his character resembled that played by Stephen Fry (brown-nosing rival) in the second series, with Fry in turn now playing a character more akin to that of BRIAN BLESSED and Miranda Richardson respectively (insane tyrant) in the first two series. This slightly convoluted game of "musical chairs" in regards to actors and characters appears however to have been of little detriment to the series.
Nancy Oleson on Little House on the Prairie is a replacement for long-time nemesis, Nellie Oleson. This is lampshaded in the episode where the Olesons adopt her, as Harriet mentions how she looks "just like Nellie" while Nels later ruefully acknowledges that she acts just like Nellie, too.
Nancy was Nellie on steroids; actually vicious enough to unthinkingly put people's lives in danger, much like their mother. When Nell returns for a visit, even she is struck by the resemblance—and put off as well, fearing her mother is making the same mistakes—which was an understatement.
The BBC version of Robin Hood appeared to be about to do this too. Season 3, episode 10 invented a backstory for Robin Hood and Guy of Gisbourne that created a mutual half-brother for the characters. Both Jonas Armstrong (Robin) and Richard Armitage (Guy) were expected to leave the show at the end of the third season, presumably to be replaced by their brother Archer. Then the show was cancelled.
Likewise, on the BBC version, the character of Marian was replaced with Kate...who had the same personality as her predecessor, only blonde and poor (and shrill). The result was cringe-inducing considering that Kate was written as arrogant, impetuous, and initially antagonistic toward Robin, just as Marian was. What the writers failed to realize was that such traits are understandable and endearing in a privileged noblewoman who had been jilted by Robin, but completely nonsensical in a peasant girl who had no reason to be any of these things.
Law & Order has always had six main characters: two detectives, their chief, the DA, the executive assistant DA, and a regular assistant DA. Given that the series lasted for 20 seasons, all six roles have been substituted as actors move on, some of them several times over. It also helps that the show is heavily story-based, and not too dependent on characterizations.
The earliest example occurred in the first episode of Season 2. No sooner was Season 1's Max Greevey (George Dzundza) gunned down that the credits start and we see Paul Sorvino's name in the credits. Sorvino's character, Phil Cerreta was a similarly overweight, older detective whose sense of values conflicted with Logan's more reckless tendencies, especially in this episode.
Law & Order: Special Victims Unit has seen this a few times; while actress Mariska Hargitay was away due to pregnancy, her character Olivia Benson was briefly replaced by arguable Canon Sue Dani Beck, who spoke fluent French, physically assaulted perps without consequence, was famous for her effectiveness in fighting crime, had a cool personal PDA/GPS system that she flashed around a few times, and had the romantic affair with Elliot that fans wanted him to have with Olivia. In general, the fandom doesn't miss her.
Similarly, the ADA's in SVU get replaced. Most people didn't mind the Alex Cabot replacement by Casey Novak (they have very different personalities), but the ADA who replaced Novak for Season 10 was a mediocre blend of both of them, with a dash of Informed Ability to boot. "They used to call me the Crusader." Fan backlash led to them bringing back Alex.
Coy and Vance replaced Bo and Luke Duke. They were such substitutes, they even had the same hair color. The following season Bo and Luke were brought back, and Coy and Vance were never heard of again.
Deputy Cletus Hogg, although his initial appearance on the show preceded Enos' departure for his own series, and he was allowed to stay on even after Enos returned.
Roscoe was also replaced briefly by two different sheriffs — including The Other Darrin himself.
In the Australian teen series Wicked Science, the girl in Toby's group, Dina, was replaced by Toby's cousin Sasha in Season 2.
Mr. Harmon, Old Mr. Grace, and Mr. Spooner replacing Mr. Mash, Young Mr. Grace and Mr. Lucas on Are You Being Served?.
Also Mr Grainger, the head of menswear, was replaced by Tebbs, Goldberg, Klein, and Grossman before they eliminated role and made Mr Humphries head of the department.
Charlie Crawford replaced Mike Flaherty as the Deputy Mayor on Spin City. The key difference was that Charlie was a Handsome Lech and Mike wasn't.
Charlie Crawford was played by Charlie Sheen, who also played Charlie Harper in Two and a Half Men. Sheen ended up getting fired from the show due to his drug problems and for making derogatory remarks about the show's creator and executive producer. Harper was killed off and replaced by Walden Schmidt, played by Ashton Kutcher. Both characters are immature womanizers.
When Gomer Pyle left The Andy Griffith Show in 1964 for his own spin-off, Gomer Pyle USMC (of "'PYYYYLE!'...'Shazam!'" fame), he was replaced by equally hayseed cousin Goober Pyle.
Up to that point, Goober was only referred to by Gomer as a running gag; his materializing as Gomer's replacement would be something like Seinfeld's Kramer being replaced by the infamous "Bob Sacamano." Weird.
Well, technically, Goober did appear in one episode ("Fun Girls") prior to Gomer's departure from Mayberry.
Warren Ferguson and (arguably) Howard Sprague, for Barney Fife.
Andy's steady girlfriend in the first season was pharmacist Ellie Walker; after she was written out of the show (apparently due to lack of chemistry between Andy Griffith and Elinor Donahue), Andy was given a couple more temporary love interests before Helen Crump was finally introduced in season 3.
When the show was retooled as Mayberry, R.F.D., Sam Jones and his son Mike essentially became the substitutes for Andy and Opie Taylor.
Uncle Albert for Grandad on Only Fools and Horses. More blatant in his first few appearances, in which he was just filling the role that Grandad would have filled if not for Lennard Pearce dying, but he soon started to be portrayed as being more physically capable and less of a Cloud Cuckoolander than Grandad, along with his navy background playing a more important part in episodes.
The long-running Australian sitcom Hey Dad..! continued for a 13th and 14th season after the titular character left, with a family friend serving as an unofficial father figure. Over its long lifespan, the show had a nearly complete changeover of cast, with replacements alternating between thinly-disguised substitutes and unexplained Other Darrins.
My Three Sons did this a lot. They replaced grandpa Bub with Uncle Charlie. Later the oldest son left so the dad adopted the youngest son's friend.
The real offenders are the early companions. Susan, Vicki, Dodo, Victoria and Zoe, while not identical in personality, all fit a "surrogate grand-daughter" model in their youth, innocence, and relationship with the Doctor (with Dodo noticeably similar in appearance to Susan and in fact one of the actresses considered for the role, though the actress was not cast for this reason alone). From the point that Ian and Barbara were both replaced by Steven, the rest of the sixties saw a stable companion model of a young heroic male and attractive young female as counterparts to the older Hartnell, and the slightly old Troughton. In the main exception of the decade, Polly and Ben were a pair, and quickly were supplemented with Jamie, the new version of the young heroic male (due to Jamie's character being a last-minute addition). Polly and Ben left after Jamie's Day in the Limelight story.
This also overlaps with Composite Character - Ian and Barbara (Ian noble and snarky, Barbara clever, worry-prone and occasionally prickly) left and were 'amalgamated' into Steven, an Action Hero like Ian but with a personality similar to Barbara's (in fact, "Galaxy 4" was originally written for Barbara and gives Steven her dialogue with only a few changes).
The Doctor's regeneration was designed specifically to avoid this. Originally there was no plans for him to regenerate he wasn't even designated an alien, it only came about when William Hartnell had to leave the show due to health issues. A producer thought it would be a novel idea and thus the Doctor as we know him was born.
The original plans for Season 7 had Zoe as the Third Doctor's companion; soon the producer decided she should be written out to give the show a Reboot and so they created Liz, a similar Hot Scientist, to replace her.
"The Invasion" is virtually a direct sequel to "The Web of Fear", but has sewer-dwelling Cybermen invading London substituting for Underground-dwelling Yeti invading London, and replaces Professor Travers and Miss Travers with a similar Mad Scientist & Mad Scientist's Beautiful Daughter pair. This was because the producer fell out with the creator of the Yeti and the Traverses and wanted to pay them as little as possible. The one returning character created by them is Lethbridge-Stewart, because Douglas Camfield wanted the actor back and having a Suspiciously Similar Substitute played by the same actor would just be begging for a lawsuit, and even he gets a promotion from his previous role and is mostly referred to by that rank.
Prop example - the Fourth Doctor started using a 'secondary console room' at one point designed to fit the gothic motif he was swiftly developing, which had a chapel-like appearance complete with stained-glass windows and gorgeous real wood panelling on everything. However, the BBC stored the set poorly and the wood warped and cracked, forcing the Doctor to revert to the previous console room set, with a Hand Wave about him redecorating the secondary console room to look like his previous one. (This also serendipitously coincided with the Doctor's characterisation going in a Lighter and Softer direction.)
Facially deformed time-travelling Diabolical Mastermind Magnus Greel in "The Talons of Weng-Chiang" was originally supposed to be the facially-deformed incarnation of the Master from "The Deadly Assassin", as the story was planned as a direct sequel to it. It ended up mutating into something else.
The Toclafane - mutated, insane, Omnicidal Maniac humanoids dependent on heavily-armed miniature tank cases to survive - were created as a substitute for the Daleks if the revival show could not get the rights to use them, as the negotiations with Terry Nation's estate were going badly. "Dalek" (titled "Absence of the Daleks") would have revolved around the audience expecting to find a Dalek, but the creature instead being the last Toclafane, the race that wiped out the Time Lords. "Bad Wolf" and "The Parting of the Ways" would have been the conclusion of their Arc and revealed that they were in fact humans from the future. The final version of Series 1 did use Daleks in this role, but the Daleks encountered in that story were built from mutated humans like the Toclafane.
Howard Attfield, who played Donna Noble's father in "The Runaway Bride," died during the filming of Series 4. They filled his role with Wilfred Mott (Bernard Cribbins), who had been created as a one-off guest character in "Voyage of the Damned" and was promptly retconned as Donna's maternal grandfather. This is not the first time Cribbins has been a Doctor Who Suspiciously Similar Substitute; in the second of the 1960s non-canon movies, Daleks' Invasion Earth: 2150 A.D., he plays Special Constable Tom Campbell, who replaces the movieverse version of Ian Chesterton who appeared in the earlier movie Dr. Who And The Daleks. Louise, the Doctor's niece, is introduced as an almost identical replacement for movieverse Barbara.
Early plans for Series 4 had a character called Penny Carter stepping in as the new companion, 'as much like Donna Noble as I can get away with' according to writer Russell T. Davies, due to his assumption that the actress who played Donna in a one-off appearance, Catherine Tate, being quite popular and busy, would not agree to return in a regular role. When Tate actually agreed to do the show after all and Donna became the full-time companion, Penny Carter did appear as a minor character, spending almost all of her screen time complaining in Donna-like fashion.
BBC Executive Meddling really, really wanted Matt Smith's Eleventh Doctor to be as much like David Tennant's Tenth Doctor as possible, fearing a more unusual character would not be as relevant and popular (there had been discussion of canning the show for good). The original proposed outfit for the character even followed a similar 90s indie kid aesthetic (by way of a pirate), but Smith strongly disliked it. The eventual character was more similar to the Tenth Doctor than many other Doctors over the years had been to their predecessors - being also a young, romantic figure with a tendency to ramble and a lot of suppressed Angst - but different enough to change the whole feel of the show.
"A Good Man Goes to War" was supposed to include Captain Jack as part of the Doctor's army, but John Barrowman was unavailable and so the character of Vastra was created to take his role - possibly why it's only in that story that Vastra shows any sexual interest in men, being exclusively lesbian otherwise.
Tasha Lem in "The Time of the Doctor" is so similar to River Song that some fans speculate that she's a regeneration of her. However dialogue in the episode - plus the fact that Tasha technically dies in the episode, being replaced by a Dalek duplicate albeit with her memories and feelings for the Doctor retained, a complete contradiction of River's fate - tends to suggest otherwise.
The web game The Doctor and the Dalek replaces the brain-damaged "good" Time War Dalek the Doctor cutely nicknames Rusty (from the episode "Into the Dalek") with the brain-damaged "good" Time War Dalek the Doctor cutely nicknames Lumpy. This is probably because fitting Rusty into the plot would be begging for problems.
Torchwood did this in Children of Earth with Lois, who fills the role Martha was joining to play had Freema Agyeman been available.
Subverted in the same miniseries when a character who seems like he's being built up to be a substitute for Owen suddenly shoots Jack in the back, and then gets shot himself. RTD says this was intentional, because he thinks it's a disservice to characters to outright replace them with a Suspiciously Similar Substitute.
In "Goodbye Sarah Jane Smith", Ruby villainously attempts to become this for Sarah Jane.
In the show's single, rather obscure, straight example, the Ancient Lights in "Secrets of the Stars" are a slightly-altered version of the Mandragora Helix from the 1970s Doctor Who story "The Masque of Mandragora". Originally, they were intended to be the same entity, but it was decided that it would be too obscure a continuity reference even by Doctor Who universe standards.
Due South did this surprisingly well, mixing in a bit of Sister Becky. One character is sent away "under cover" while the main character is out of town. The replacement is introduced as someone pretending to be that character, in order to maintain his cover.
For bonus points, the replacement is almost nothing like his predecessor, with almost everybody except Fraser seeming to be unaware of this
A few years earlier, Stephen Fry was supposed to be the second regular on Whose Line Is It Anyway?, but backed out at the last minute (he didn't actually like doing improv that much). He was replaced by...Tony Slattery.
Stephen Fry and Tony Slattery were both members of the Cambridge Footlights at the same time, by the way. And Slattery took up the position of Footlights president after Fry's good friend and frequent collaborator Hugh Laurie served in that position for a year.
At the end of Season 2, NCIS agent Kate Todd is shot and killed by Ari Haswari, a Hamas terrorist working undercover within Mossad. Then at the beginning of Season 3, Mossad agent Ziva David, Ari's sister, joins the NCIS team as a Liaison Officer. Ziva resembles Kate physically- both are slim, brown eyed brunettes. And Ziva quickly picks up Kate's habit of engaging in rivalry, banter and Unresolved Sexual Tension with NCIS agent Tony DiNozzo. Otherwise, Kate and Ziva are quite different characters, but this is not a case of The Other Darrin.
The fifth season ends on a cliffhanger which implies that Tony, Ziva, and McGee will all be substituted, and, indeed, the sixth season premiere shows Gibbs leading a new team, with establishing shots helpfully indicating which of the previous characters' niches the new agents fit into. Interestingly, the new team has most of the worst qualities of the characters they're replacing—Langer is a meaner Tony, Keating is a wimpier McGee, etc. The trope is then fairly quickly subverted and by the end of the second episode of the season, the team is reunited and back in business.
Subverted in the 7th season opener when the team interviews replacements for Ziva. Two don't live up to their hype, and one came in at the wrong time. Ziva returns at the end, at least physically.
Also subverted when Ziva leaves for good at the beginning of Season 11; her replacement, Ellie Bishop, is nothing like Ziva or Kate.
Sliders was rife with substituting toward the end, though most weren't very similar to those they replaced. However, Quinn got substituted when actor Jerry O Connell left, by way of The Nth Doctor by being "fused" with 'Mallory' (his non-identical counterpart from a parallel universe), at the same time Colin wasPut on a Bus. But with a different personality and face, Quinn Mallory's substitute isn't the other Quinn Mallory. Hot Scientist Diana Davis takes his role as the scientific brains on the team.
A certain segment of the fanbase believes that Arturo was substituted byhis own alternate. The episode that this happens in allows for that interpretation as Arturo's villainous duplicate tries to replace him so he can escape his own world and just before they slide they are having a classic "which is the real one?" battle, and after the slide the Arturo who was left behind gives a quiet, "Oh, my God." Worse yet, Series creator Tracy Torme has tormented fans by saying that he knows which Arturo made the jump, but will never reveal it.
Done by necessity quite a lot on gentle old dears' British comedy Last of the Summer Wine, as elderly cast members die off with inconvenient regularity. (Currently only one member of the original central trio is still alive).
Done on 'Allo 'Allo! when Mimi and Captain Bertorelli appeared as substitutes for Maria and the German Captain Hans respectively — in particular, Mimi was at least as short as Maria and both had fiery tempers. It allowed them to continue the gag of Mimi/Maria having to get a stool to stand on in order to hug René. Later, Monsieur Leclerc was replaced by his twin brother after the original actor died. Captain Bertorelli and the second Leclerc were then replaced in a The Other Darrin manner.
Also parodied in the series, when René's death was faked and he was forced to pose as his own Suspiciously Similar Substitute twin brother for the rest of the show.
René: "I am also named René."
The German police drama Siska did this when they replaced the eponymous lead character with his never-before-mentioned brother after he was killed off.
Luka Kovacs for Doug Ross. Dave Malucci also, as he took on the brash, reckless, rebellious character traits of Doug.
Similarly, Abby Lockhart for Carol Hathaway. She was introduced as Carol's OB nurse during her labor, but promptly replaced her in the ER after she left. Not only did she immediately start dating Luka, Carol's ex (and aforementioned Doug Ross replacement), but she was even given the aborted nurse-to-doctor storyline (admittedly with some differences; Carol had always been an RN but decided to study for and take her MCA Ts just to see if she could pass them. Although scenes were filmed with Carol starting medical school, actress Julianna Margulies was unhappy with the storyline as Carol had always been passionate about nursing and she felt it was out of character for her to switch careers. By contrast, Abby was introduced as a wannabe doc who took nursing shifts to pay for med school. She dropped out not long after her introduction due to lack of funds, but always intended to go back and finish, which she eventually did, becoming a fully-fledged doctor).
Many new characters were like this, being introduced in the plucky Naďve Newcomer mold of Carter (Lucy, Gallant, Neela, even Dr. Wise in the series finale), or the "tough & abrasive go-getter" type (Kerry, Morretti, Brenner, Banfield)
Married... with Children: Straitlaced banker Steve Rhoades (David Garrison) was Marcy's husband for four seasons, and then was replaced by pretty-boy Jefferson D'Arcy (Ted McGinley) when Garrison wanted to leave the show to avoid being typecast. This was rather a subversion because Jefferson was a completely different character than Steve.
Everwood, for some extent at least: Linda and Amanda are both facing a tragedy of sorts, both feel uneasy around Nina (foreshadowing, much?) and both have a similar relationship with Andy: the rocky start, people against the affair, having a hard time fitting in Andy's family life, and finally breaking up over something directly related to the aforementioned tragedy. Amy's best friends, Laynie and Hannah (who never appeared simultaneously, although they'd be best friends themselves in Grey's Anatomy, same actresses, different characters), also share some traits: tragedy again (the common denominator for everybody in the show), introverted, both have an older brother (one of them dies and the other has a strong chance of inheriting Huntington's), both are somewhat "dark" and both girls click with Ephram instantly (Laynie actually dates him, Hannah is more a best friend / neighbor / like sibling type). Last but not least, Stephanie is in many ways a short-lived Madison II (college-girl, very different from Ephram, great with Deliah, kind with Amy in spite of her (Amy's) jealousy).
Teachers initially both justified and averted it. It justified it because, in a school, teachers genuinely do come and go and get replaced, so it never seemed odd to have cast changes between series. They averted it by not replacing characters with direct clones, particularly after main character Simon left and the show became an ensemble piece. Unfortunately, after the third series, ensemble darkhorses Kurt and Brian left, along with Simon's arbitrary replacement Matt, to be replaced by Damien and Ben, substitutes for Kurt and Brian, and Ewan, a substitute for Simon. Cue Seasonal Rot and no fifth series.
Dr. Peele of American Gothic was this, replacing Dr. Crower—only to then be sent veering off in a different direction by being paired up with the Femme Fatale, then relegated to backburner status for the rest of the series.
Sandy Duncan's character on The Hogan Family, which was Valerie before Valerie Harper quit.
Neil Morrissey as Tony Smart from series 2 of Men Behaving Badly, replacing Harry Enfield as Dermot Povey. Since this happened on ITV, and the show only became popular after the third series was taken up by The BBC, most viewers have only the vaguest idea there ever was a Dermot Povey. (In one Clip Show, a single scene from series 1 is shown, prompting Tony to ask "Who was that?")
That '70s Show replaced Eric and Kelso with Randy, who had similar personality traits of both other characters.
In Blake's 7, substitutes are always the same gender as the outgoing character, for no particular reason but to make up the numbers. Jenna is replaced by Dayna, Blake is replaced by Tarrant, and Cally is replaced by Soolin. Slightly subverted in the episode 'Rescue', though, where the tough guy and the female pilot are replaced by a male pilot and a tough chick, respectively.
In Frontline, each season features a new Executive Producer, all of whom are equally amoral but manipulate people in slightly different ways.
In Gilmore Girls, when Chad Michael Murray (Tristan DuGray) left for a slew of other WB projects (including Dawson's Creek, a failed Lone Ranger pilot and then eventually One Tree Hill). This left a void in the Rory/Dean/Other love/hate triangle. The void was soon filled by Jess Mariano (Milo Ventimiglia).
Although Jess's character was VASTLY different from Tristan's, and the dynamics of the relationship between him and Rory were much more even.
Logan Huntzberger, however, was just Tristan 2.0.
Monk did this when Traylor Howard was introduced as Natalie Teeger, replacing Bitty Schram's character Sharona Fleming as Monk's assistant midway through season 3. The next few episodes were very obviously written for Sharona, with the only real difference in the characters being Natalie calls him "Mr. Monk" instead of "Adrian." (Well, almost all of the time) This gets especially weird when she states that she's never seen Monk's feet like that's a big deal, despite having only taken the job in the previous episode. The point at which the writers ran out of their previous scripts and were able to start creating material specifically for Natalie (mostly involving her dead husband at first) is very, very clear, and happens some time around "Mr. Monk and the Election" or "Mr. Monk and the Kid".
Due to the death of Stanley Kamel (Dr. Kroger), Hector Elizondo has taken on the role of a new psychiatrist for Adrian Monk.
Get Smart (the original show) did this for the episode "Ice Station Siegfried." Don Adams had a root canal and couldn't be there for the shooting of one episode, so the writers created Agent Quigley, who acted exactly like Maxwell Smart and was also attracted to Agent 99, to replace him for one episode. He was never seen nor mentioned again. Incidentally, the script for "Ice Station Siegfried" was so bad that Adams purposely scheduled his dentist appointment so that he would miss the filming of it and not another Season 5 episode.
Dads Army introduced Private Cheeseman as a substitute after the sudden death of James Beck, who played Walker. The character fast became a Scrappy and was written out after only one season.
Although not as obvious as some other examples, the producers wrestled with who they could get to replace Cordelia's snarky truth-telling character (who had left for Angel, where she'd undergo a whack of Character Development and change personalities anyway). At first, when getting wind of the popularity of Spike and deciding to keep him on, they'd thought to have him do it, but they later decided to use Anya, a previously one-episode appearance, to become a regular and take over Cordelia's role in the group.
While we're at it, Spike, the Vampire-fighting-for-good, is curiously similar to Angel. Eventually even the slightly-different motivation, the behavior-dampening hardware placed in his brain, is written out and he is given a soul just like his counterpart. And yeah, they both date Buffy. Their personalities are not remotely similar, though.
The trope was inverted with Kennedy, who was deliberately made very different from Willow's previous love interest Tara. Perhaps not the best idea, as Kennedy was pushy, arrogant, and abrasive where Tara was shy, gentle and empathetic. She was not received well.
There's a textbook subversion in season 1, after Angel loses Doyle. He complains that his link to the Powers That Be is gone, only to be told that "whenever a door closes, another opens." Enter a very Doyle-like character...who turns out, after a series of misdirections, to be the Monster of the Week, not the new sidekick. Cordelia gains Doyle's powers and role.
Doyle himself was a Suspiciously Similar Substitute for Whistler, a character who appeared briefly in flashbacks in Buffy's second season finale and recruited Angel to the side of good. Both are sarcastic demons (half-demon, in Doyle's case) who work for the Powers That Be. Doyle was originally intended to be Whistler, but the actor was unavailable when the show was greenlit, so they reworked him as newcomer Doyle. In "City of" Doyle even wears a hat similar to Whistler's iconic hat.
Joss Whedon admits that after Cordelia went insane, fell into a coma, and was absent in the show's final season, the writers felt that the show had lost an important puzzle piece. Enter Harmony. Dim-witted, blonde, and completely peculiar vampire who seems to carry the personality of Cordelia circa Season 1. They even went as far as adding her as a main character in the opening credits for the final six episodes. Though since Harmony had been there since the very first episode of Buffy (and being one of the Cordettes) her character was already known and accepted. Word of God is that Harmony was supposed to be a recurring character once she arrived on Angel...but they forgot about her until the final season. Then, they ended up having her in every episode, so it was somewhat necessary to make her part of the main cast.
For Season Five, Eve served the part of Cordelia that was to play Angel's foil. Spike as in Buffy Season Four came on to give the much-needed sarcastic remarks. Illyria, later, became the one who provided conflict by always saying it like it is.
Eve also effectively replaced Lilah Morgan as the untrustworthy senior female at Wolfram & Hart, as she herself commented on in her first scene.
In Judging Amy, Dan Futterman played Vincent Gray, Amy's highly intelligent younger brother, in episodes 1 through 51, when he left the show. He was soon substituted by Kevin Rahm in the role of Kyle McCarty, Amy and Vincent's highly intelligent second cousin who had much of the same intelligence and mannerisms as Vincent. With Kyle's introduction, it was explained that Vincent and Kyle had been roommates and spent much of their younger years together. Vincent returned to the show in episode 100, and effectively reverse-substituted for Kyle who left the show in episode 118. Vincent remained for the rest of the show's run.
Jeffrey Coho from Boston Legal is an interesting example, in that he was the substitute for a character who was still on the show. Over the first two seasons, the main character Alan Shore transformed from being a rather-slimy-lawyer-with-a-deeply-buried-heart-of-gold type to a civil rights crusader. Jeffrey Coho was brought onto the show at the beginning of Season 3, and was identical in personality to Season 1 Alan, even down to his politics and his feuding with Brad Chase (except, mercifully, for the friendship with Denny Crane, which was only ever Alan's).
Benson — Rene Auberjonois' Clayton Endicott III was a clone of his predecessor, Taylor (albeit with a more impressively pretentious name).
Hill Street Blues — When Michael Conrad died after Season 3, his Sgt. Esterhaus was replaced with Robert Prosky's Sgt. Jablonski (who was even given a similar catchphrase to close out the briefing at the top of each episode).
Jolene didn't actually replace Flo per se. When Polly Holiday left to star in the short-lived spinoff Flo, she was replaced by Diane Ladd (who played Flo in the movie), although on the TV show, she played an original character named "Belle Dupree", another sassy, sarcastic middle aged southern gal. Eventually Diane left, and SHE was replaced by Jolene.
Inverted, somewhat, on All in the Family: The character of George Jefferson was expressly written for Sherman Helmsley, who was unavailable at the time the show's early seasons were shot due to his appearance in a Broadway musical; the character of George's brother, Henry Jefferson, was devised as a placeholder until Helmsley became available in Season 4 (although George was "on" the show as an offscreen character in the earlier seasons).
Phil in Corner Gas replacing Paul as the Cree with long hair and the four letter name that starts with P and ends with L who works as the head bartender. The only difference apart from name is that Phil looks older and has a deeper, less enthusiastic voice.
When Mickey left Hustle after season 3, Billy was introduced as a Suspiciously Similar Substitute for Danny, with Danny taking up Mickey's role. In season 5, Mickey's back and the Danny/Billy role is taken by Sean, with his sister Emma as the new Stacie.
This was because Mark Frankel's character Julian Luna had quickly taken over as star of the show after proving far more popular than the original lead — C. Thomas Howell's Frank Kohanek — who was intensely disliked by fans and critics alike. Frank was supposed to be written out in Season 2, and Julian made the lead. Without the fan favorite, the producers believed that the show was too weak to continue.
Tiffani Thiessen's Valerie Malone on Beverly Hills 90210. Valerie was introduced after Shannen Doherty was fired from the show and was a brunette of similar temperament to Doherty's Brenda who lived in her room and slept with her ex-boyfriend. Her twist was that she was a pot-smoking 'naughty girl', as the characters in the show would constantly remind us.
After Howard Hesseman left Head of the Class in 1990, Billy Connolly's character substituted him for the show's final season.
Diff'rent Strokes: After Edna Garrett's departure for her own spinoff (The Facts of Life), she was replaced as the Drummonds' housekeeper with Adelaide Brubaker...who was substituted, in turn, by Pearl Gallagher.
Mrs. Garrett was eventually substituted herself on The Facts of Life by her sister, Beverly Ann Stickle.
The Love Boat replaced Julie McCoy with her sister Judy as "Your Cruise Director," following actress Lauren Tewes' departure from the show due to cocaine addiction.
Sophie's cousin Barney in the fifth series of Peep Show is a fairly obvious replacement for her brother Jamie from series four; they look similar, are both musicians, both obsessed with Jeremy, and Barney even hangs around with Sophie's father for no explained reason.
Season three of MI High replaced Daisy, Blaine, and their boss. A number of minor characters are also gone as well. In fact the only characters who have been carried over from the last season are Rose, The Grand Master and the school headmaster.
The third series replaced Lenny Bicknall with Frank London, both retired superspies posing as a high school caretaker.
Knight Rider replaced Wrench Wench Bonnie Barstow with April Curtis for the second season, then brought back Bonnie the next year.
Happy Days, upon the leaving of Ron Howard, brought in a family friend named Roger who replaced the 'straight-man' tendencies of Richie.
There have been seven Iron Chefs: Chen Kenichi (Chinese), Hiroyuki Sakai (French), Masaharu Morimoto (Japanese), and Masahiko Kobe (Italian) are the ones American viewers are most familiar with. The dubbed version tried to push the idea that Morimoto was the direct successor to Rokusaburo Michiba, the original IC Japanese. In truth, Morimoto was a substitute to a substitute: Michiba's replacement was Koumei Nakamura (Who can be spotted behind Chairman Kaga in the opening credits, where Kaga is standing behind the pile of strawberries). There's also the original IC French, Yutaka Ishinabe (whose portrait can be spotted in the opening panorama).
Season 7 introduces Janis Gold, a frumpy bespectacled computer technician, who is the FBI's version of Chloe. They bring Chloe back for a few episodes, and they don't get along.
The character of Mandy is another example. If the producers couldn't get Mia Kirshner the actress who played her they created another sexy terrorist. Season 4's Nicole is a prime example, because she behaves in EXACTLY the same way as Mandy would, she has sex with a character to get him on side, then reveals her true colors. Mandy did more or less the same thing in the first episode. Which is amusing in itself considering Mandy actually did return at the very end of the fourth season.
Olivia Taylor's only real existence on the show was to essentially play Sherri Palmer to her mother Allison's David: The former is a corrupt, manipulative bitch family to the latter who is the President and very much a strong moral force for the country.
The show replaced two characters in the ninth season, with Ray Langston, and Riley Adams, though they seem to be the latter type, each having their own character traits.
DB Russell is said to be a straighter version of this, because he has some similarities to Grissom, though not so close that it screams "Grissom Light".
By comparison, CSI: NY replaced Aiden Burn with another occasionally-sarcastic female character, who was even suggested to be in a relationship with the same character, at least until she was Killed Off for Real. Her other traits were added to a previously-existing background character, who occasionally takes Don Flack's place. Later, a new recurring female detective was brought into the series, and appears to be a Suspiciously Similar Substitute for the original Suspiciously Similar Substitute. She's even becoming Flack's new love interest.
While the original ducklings still appear on House, their roles as, well, ducklings have been replaced. By Taub, Kutner and Thirteen, who are superficially similar to the original three characters. Their exact personalities don't line up but House admitted that he hired them based on the same dynamic he had with the earlier team. Interestingly enough for the trope, the previous actors didn't leave the show, they just added more cast.
NYPD Blue is the master of this trope, having replaced Andy Sipowicz's partner three times. Jimmy Smits replaced David Caruso when the latter decided he was too big to do the show. Rick Schroeder replaced Smits. Mark-Paul Gosselaar replaced Schroeder. Gosselaar and Schroeder are the best examples here, both having similar physical make-ups and similar character personalities.
Battlestar Galactica replaced Billy Keikeya with Tory Foster. This is actually the only Battlestar example. Given the improvisational nature of the series' writing it's unclear if Billy would have followed a similar arc to Tory, had Paul Campbell remained on the show.
Well, at the very least, he probably wouldn't have slept with Anders and Baltar.
This trope is played straight or averted, as the lack of similarity between the two characters is noted by Roslin and Adama in Tory's very first appearance.
In The George Lopez Show, Carmen is replaced with Angie's niece Veronica Palmero because of creative differences between Carmen's actress, Masiela Lusha, and George Lopez. Veronica is the same as Carmen, only more shallow and with a sadder story.
The character of Laverne was killed off, due to the writers being under the impression the 6th season would be the last. It wasn't. Cue Nurse Shirley, who is played by the same actress that played Laverne! This is lampshaded when JD nicknames her "Laverneagain." The hospital's fake website uses the exact same picture for both nurses' profiles. It's actually a subversion, since what little personality the writers had a chance to give to her dialogue, and a good deal of the acting Aloma Wright did, was meant to create the impression of an anti-Laverne. Laverne and Shirley?
For the last season, the main character is JD and Elliot combined (narrator, daydreaming delusions, blonde, crazy, likes horses, bullied by Dr. Cox...) and Denise is also given some more obvious JD traits after he leaves. Denise and Drew sort of become the new Jordan and Dr. Cox.
According to some, Kochanski was this for Rimmer on Red Dwarf. Others thought Kochanski replaced Kryten, while the latter became Rimmer's replacement.
Also inverted — Rimmer is killed off in the first episode and replaced by a hologram, portrayed by the same actor. Hologram Rimmer was written out of the story in Series VII after Chris Barrie chose to leave the show. He returned in Series VIII to play the revived original Rimmer.
Subverted with Pree, who is obviously set up to be a replacement for Holly, only to turn into the Monster of the Week.
After the death of Bea Benederet, the mother and hotel manager from Petticoat Junction, June Lockhart was cast as a new town doctor who took up residence in the hotel. Although she was clearly not the girls' mother, and the girls were all well into adulthood by that point, she carried on Benederet's function as motherly advisor, and the town's most sensible resident.
After season 1 of Mission: Impossible, team leader Dan Briggs was replaced by Jim Phelps. After season 3, Rollin Hand was replaced by "The Great Paris." Replacements were seamless, since the characters were constantly playing roles within the show, and were purposely written to show a minimum of personality outside their jobs.
Jim was actually rather different in personality from Dan, a more friendly and avuncular sort whereas Dan was a hardass with a ruthless streak. Also, Dan sometimes supervised the missions remotely rather than joining them, whereas Jim was always part of the mission team. Jim was also more suited for romantic roles than Dan. However, Paris was an exact replacement for Rollin, with the exact same skill set (disguise, magic, cheating at cards, pickpocketing). In his first season (year 4), he was Rollin by another name, but in season 5, when the show got more character-driven for a time, he developed a distinct, more casual and "hip" personality.
In addition, The Chick in the Five-Man Band started out as Cinnamon, who was replaced by a parade of guest stars in Season 4, Dana in Season 5, and Casey in Seasons 6-7 (with Mimi briefly serving as a Temporary Substitute). Averted somewhat with Casey, who was not just the femme fatale but also replaced Rollin and Paris as the team's makeup master, since budget cuts required reducing the cast size. The show also attempted to replace Willy with a doctor named Doug, but Willy was Saved by the Fans.
Averted, kind of, in Bones. At the start of season 3 we were given recurring character Sweets, a young, clever psychologist. He became a regular with his name added to the opening credits at the end of the season when Zack, the young, clever anthropologist, left the show. Averted in that the characters don't have much more in common and that Sweets is very well-liked. Also averted in that Zach's in-universe role (anthropology student in the lab) is now pointedly rotated between five different guest characters, because everyone agrees that Zach is irreplaceable anyway.
Sully could be seen as a variation of this trope. Booth had not left the series, but Agent Tim Sullivan was brought in as a replacement boyfriend for Brennan-but he was so much like Booth that the fans dubbed him "Booth Light".
Seen repeatedly in Gene Roddenberry's Earth: Final Conflict, due to the show's unusually high cast turnover rate. In fact, the only character to last through all 5 seasons was series villain Agent Sandoval.
The character of Tyr, a Nietzschean who could not be trusted was replaced by Rhade, a Nietzchean who could not be trusted. Tyr went on to become a complete wuss when the actor guest-starred in later episodes.
The character of Doyle in the final season is also somewhat of a replacement for Lexa Doig's Andromeda when her role needed to be reduced due to the actress's pregnancy. Doyle provided a love target and protector for Harper, among other regular Rommie duties.
Doig similarly played a replacement doctor in Stargate SG-1, though her character was less-developed than the one she replaced, Dr. Frasier, and the replacement was not immediate.
Doig's husband is also Michael Shanks, whose Daniel was SG-1's original character substituted for with Jonas Quinn.
Lexx couldn't get the actress who played Wist back, so they created a second gorgeous blonde predator with a childlike demeanor in Lyekka.
The Tick suffered from a number of poor copies meant to be substitutes when Fox failed to get the rights for any characters besides The Tick and Arthur. But given that it was Fox, no one was really surprised as the show's days were numbered from day one. Though, to give credit where credit is due, Bat Manuel is one of the funniest television characters ever. Even better the actor who played Bat Manuel in the live action version of The Tick played the Mayor in the Batman movie The Dark Knight.
Ashley's ultimate demise in Sanctuary was particularly predictable because in the two episodes preceding it, they were already gearing up her replacement.
In The Thick of It series three has a new Minister For Social Affairs — Nicola Murray replacing Hugh Abbot. Her only points of difference with her predecessor are that she's a woman, and that she's not best friends with her main ministerial advisor. This is entirely justified, as the premise of the show is that all politicians are the same.
On Leverage, Gina Bellman's pregnancy required a hasty write-off of Sophie before she started showing, so she was replaced for half a season by Tara Cole (played by Jeri Ryan).
Carried out with style by British fantasy show Hex, where new girl Ella, an experienced witch, shows up at the start of the second season and by the end of the second episode has stabbed original lead witch Cassie and taken her place as the show's main character. She goes on to have an almost identical doomed relationship with demon spawn Malachi that Cassie had with demon Azazeal in the first season. To round things off, Malachi is Cassie and Azazeal's magically-aged son.
Drop the Dead Donkey replaced Alex, the one sensible person in the Globelink office, with Helen, a virtually identical character, at the end of the second series. Both of them even had one-night stands with Dave (despite Helen being a lesbian).
Averted in Mutant X, which saw Lexa replace Emma at the start of the final season after Emma's death in the previous finale. Counts as an aversion because, rather than the new character being designed to fill the superpowered gap in the team the old one had left, telempathic Emma was replaced with light-manipulating Lexa, whose personality, loyalties, and storyline were radically different to Emma's.
To quote Wyatt Cenac on The Daily Show: "WHY WOULD YOU THROW RUDY UNDER THE BUS?! SHE'S STILL THE SAME RUDY!!"
Really head-spinning example from THE PAPER CHASE: When the study group is formed during the pilot episode, one woman is included. In the very second episode, that character's place in the study group, with no explanation, has been taken by another woman, Logan, who remains a major character throughout the series.
On MythBusters, Kari Byron went on maternity leave, and was replaced by Jessi Combs for a few months. The original Build Team was Kari, Tori, and Scotty (Wrench Wench) who left the show under "personal reasons" and was replaced by the now better known Grant. And there is also Christine, a "Mythtern" before the Build Team came into play, who directly assisted Jamie and Adam and had a certain resemblance to Scotty.
Emily Prentiss and David Rossi were replacements for Elle Greenaway and Jason Gideon respectively. Both characters were initially hated by many fans, but gained pretty good fanbases the longer they remained on the show.
The trope is played straight with Prentiss, but not Rossi. Word of God from creator Ed Bernero on the "About Face" commentary says they wanted to make him as least like Gideon as possible, so they made him an egotistical wannabe rock star of a profiler who doesn't really "do" teams, and the first thing he does is shoot a bird. Jason Gideon was part ornithologist and part birdwatcher. Many times throughout Mandy Patinkin's run you would hear and see references to his characters' love for birds. A Take That indeed!
And now, since JJ's departure, there will be another new character joining the team—meet Ashley Seaver , FBI cadet and based on previews, the daughter of a serial killer. Yes, she does look like JJ superficially, but whether is she a good, distinct, well-drawn out character in her own right (despite the physical similarities) or a Scrappy Mary Sue copycat replacement will be determined soon when her first episode airs. Subverted by the fact that the majority of the fanbase disliked Seaver prompting the return of JJ (and Prentiss who left at the end of last season).
Tough, dark haired multilingual Elle Greenaway leaves after season 2, to be replaced with tough, dark haired, multilingual Emily Prentiss. Emily Prentiss leaves the team at the end of season 7, and is replaced in season 8 with tough, dark-haired, at-least-bilingual (knows ASL) Alex Blake. There seems to be a trend here...
Speaking of Profiler, for that show's final season, exit Ally Walker, enter Jamie Luner.
Exit off-screen nemesis Jack, enter off-screen nemesis Damian Kennasas.
A few from Neighbours, though the straightest examples may be Tom Ramsay replacing his brother Max, and Oliver Barnes being hastily written in to replace his brother Will/Sebastian, even taking over his whole character arc.
Besides The Other Darrin, Roger Davis, Alias Smith and Jones replaced the character Clementine "Clem" Hale with Georgette "George" Sinclair. Probably a case of the writers recycling scripts already written for the other character.
The German soap opera Alles Was Zahlt originally dealt with Diana Sommer, who was a plucky blonde delivery girl turned up-and-coming figure skater. In the first episode Diana was sort of hit by a car... which led to the Meet Cute introduction to her boyfriend Julian. After Julian died and the actress playing Diana decided to leave the show, a new character was introduced: the plucky blonde circus performer turn up-and-coming figure skater, Stella. Upon arriving in town her car broke down, which meant she almost got rear-ended by her immediate love interest, Lars. It wouldn't be so bad if Stella and Lars were bearable, but unfortunately, they're not.
Carla Borrego for Maddie Magellan in Jonathan Creek. And then Joey Ross for Carla. All female investigative journalists (of a sort; Carla presents a Crimewatch-style TV show and Joey runs a paranormal website) who march into situations and take charge, leaving Jonathan to fade into the background, and are eternally exasperated with him. The main difference with Joey is that her relationship with Jonathan isn't based on UST.
Agent Shaw on Chuck seems pretty similar to Bryce from Seasons 1 and 2. They're both romantic rivals to the lead character, they both mentor him on how to be a spy, and they both are super spies.
When Nickelodeon's variety show All That began, Katrina Johnson was easily the youngest-looking cast member and was mostly used to play a variety of little girl characters. In Season 3, with Katrina looking too old to pull off these roles, Amanda Bynes was added to the cast to fill the void. Katrina left the show entirely later in that season.
Designing Women: Charlene was replaced by her sister Carlene, who was about as similar as you can get.
Oddly played on Saved by the Bell. After losing Jesse and Kelly the producers introduced biker chick Tori who picked up Kelly's role as Zach's love interest. That still left a gap though, so rather than introduce new characters they transferred Jesse's brains and Kelly's popularity to Lisa who overnight leapt from average intelligence and popularity to straight A-student and homecoming queen.
More so on Saved By The Bell: The New Class, most blatantly in their first season. The new youngsters were virtual carbon copies of their old-class counterparts: Scott for Zack (even breaking the Fourth Wall in the same way), Weasel for Screech, Tommy D for Slater, Linday for Kelly, and Megan for Lisa and Jessie (due to her being Weasel's unrequited crush, as well as the smart one in the group).
White Collar introduced FBI agent Diana Barrigan in the pilot, but when the actress had other commitments, she was replaced without explanation by the character Lauren Cruz. (Who was subsequently re-replaced without explanation by Barrigan in season 2).
Diana took a job in Washington, DC because it's where her girlfriend was from, and decided to come back to New York. Lauren left with no explanation.
Charlie's Angels. At the end of Season 1 Farrah Fawcett left the series and her character, Jill Munroe was replaced by her kid sister Kris. The show's ratings soared after that.
Subverted in NCIS: Los Angeles. Originally the team was to be headed by agent Lara Macy, played by Louise Lombard, but after apparently she didn't test well with audiences in the pilot, she was replaced by Hetty Lange, played by Linda Hunt. They are nothing alike.
In Midsomer Murders, DCI Barnaby was replaced by... DCI Barnaby (his cousin, who had the same rank and personality, but was played by a different actor). Also, he had already changed his sidekick twice.
In the second season of In Treatment Luke and Bess, a couple whose divorce was harming their son, were clearly substitutes for Jake and Amy in the first season. This is because, in the Israeli series the show is based on, the corresponding couple's arc continued into the second season.
The Season 2-4 recasting of 3-2-1 Contact: Miguel=Marc, Robin=Trini, Kathy=Lisa.
Played with on Tremors: The Series when Michael Gross was unavailable for shooting. The female scientist who appeared in the episode was given a personality Suspiciously Similar to Gross's Burt Gummer, a similarity which was Lampshaded by the other characters, although she didn't perform his usual in-universe functions of shooting or blowing up monsters.
Annie replaced Fi as the protagonist in the final season of So Weird. Like Fi, Annie had paranormal encounters which she posted on a website. The "twist" was that she was a singer.
Averted and played straight by The Red Green Show. The marina owner changed from the reasonably-built but lazy Glen Brachston to the overweight and lazier Dwight Cardiff. However, they averted this with the role of animal control officer: the original one, Garth Harble, loved animals, while replacement Ed Frid was terrified of them.
Sarah Page was killed because her actress couldn't continue acting for the show, and was replaced by Jess Parker. However, their roles are very different; Sarah was an expert in mythology and ancient cultures, while Jess is a techie and team coordinator.
Sarah in turn replaced Jenny Lewis, who was an alternate-timeline duplicate of Claudia Brown, played by the same actress but with a completely different personality and role, an inversion of the typical Suspiciously Similar Substitute.
The series has also been through three different leading men and two different tough-guy supporting men. Only three cast members have stayed with the show through its entire run. The leading men are a particularly interesting example of this. With the first switch the authors went for a genuine attempt to not make the substitute suspiciously similar, and in fact the character changed the entire tone of the series. When this second leader was in turn switched out they brought in a replacement that was suspiciously similar to leading man number one, up to and including his accent. The tone of the series also switched back, becoming particularly obvious when number two reappeared for one more episode.
Reviews of The X Factor's new judges Kelly Rowland, Tulisa, and Gary Barlow recall up their respective predecessors, Dannii Minogue, Cheryl Cole, and Simon Cowell. Some reviewers even noted that Tulisa even physically resembled Cheryl in terms of looks and personality.
Upstairs Downstairs replaced Elizabeth, daughter of Sir Richard and Lady Marjorie Bellamy, with Georgina, the daughter of a couple killed in the Titanic disaster alongside Lady Marjorie. The changeover wasn't immediate, and demure, idealistic Elizabeth had a very different character to the louche Georgina, but Georgina filled the same role, so it may count. Lady Marjorie's role went through two changes as well, with Hazel and then Virginia Bellamy taking over the position of mistress of the house. Downstairs, after Emily's suicide, the show also went through a handful of identikit kitchenmaids before settling on the hapless Ruby.
On Fox's New Girl, the character of "Coach" (Damon Wayans, Jr.) appears only in the pilot. By the time the second episode rolls around, we instead have "Bishop," (Lamorne Morris) another young, handsome, goateed, athletic African-American roommate. The switch is given something of a Hand Wave, with the explanation that Bishop is the "real" roommate, and that Coach was just subletting while Bishop was off playing pro basketball in a Latvian league. The actual reason for the switch is that Wayans shot the pilot while his ABC show Happy Endings was on the cancellation bubble, and between the pilot being shot and the show being picked up as a full series, ABC decided to renew Happy Endings...Which did the same for Wayans' contract.
Leonard Rossiter's final role on UK television was as a supermarket manager in the dreadful sitcom Tripper's Day. After his death, he was replaced by Bruce Forsyth and the show was renamed Slinger's Day. This was even worse than the original but was somehow renewed for a second (six-episode) season and crossed the Atlantic to become Check It Out.
Averted in Twin Peaks, when Kyle Mac Lachlan talked the producers out of turning teenage sexpot Audrey Horne into the love interest for his character, Agent Dale Cooper. Instead, they introduced Heather Graham as Annie ... a formerly suicidal former nun. Definitely not a teenage sexpot.
Amy Amanda Allen was put on a bus and replaced for ten episodes by Tawnia Baker on The A-Team.
One episode of El Chavo del ocho featured Don Ramón's cousin Don Román. Román practically did and suffered like his cousin did in a similar episode.
Mitchell, a reformed vampire with a troubled past who's sworn off blood and lives alongside a werewolf and a ghost, was killed off at the end of Series 3. Series 4 replaces him with Hal... a reformed vampire with a troubled past who's sworn off blood and lives alongside a werewolf and a ghost.
At the same time, George, the resident werewolf, also left. His role in the house was replaced by another werewolf who had almost nothing in common with George. The reason? Tom, his replacement, had been a recurring character since the start of the third series. Zero new characterization was required.
In Misfits, all main characters from the first two series have been replaced over the course of series 3 and 4 by characters who occupy similar roles in the ensemble, but have different enough personalities.
Nathan left after Series 2, and was replaced by Rudy, an equally mouthy character who, like Nathan, has the habit of saying outrageous things. Subverted slightly in that Rudy is a more complex character with multiple facets (made literal different people by the Storm).
Simon, Alisha and Kelly left after Series 3. Series 4 introduced Simon (another socially awkward guy with hidden depths), Abby (another promiscuous party girl with hidden depths), and Jess (Another no-nonsense, rude girl). Note that despite being Kelly's Spiritual Successor, Jess takes Alisha's place romance-wise, and, just like Alisha, starts dating the handsome/athletic guy in the gang (Curtis and Alex, respectively), before ending up with the apparently weirder one (Simon and Rudy, respectively).
Series 4 introduced Alex, the handsome barman, and then killed off Curtis the athletic barman. Alex joined he gang full-time for series 5.
A rather tragic example occurred in the final season of NewsRadio (and the only example in the whole series- the other character who left was simply Put on a Bus and never replaced). Max was brought in to take over the role that had been filled by Phil Hartman as the over-egotistical Bill Mc Neil. Unfortunately shortly after the completion of season 4, Hartman was the victim of a Murder-Suicide by his own wife, and for the final season Jon Lovitz joined the cast in a similar role as Max. Incidentally Lovitz had been a close to Hartman and joined the cast because he wanted to pay homage to his friend.
The final season of Ballykissangel introduced the elderly farmer and pub regular Louis Dargan (Mick Lally) after the death of Birdy Sweeney, who played elderly farmer and pub regular Eamon Byrne. Unlike Eamon, however, Louis was never important to the plot and never spoke an intelligible sentence.
In season 3, many of the original cast (and the one's with the largest, most vocal sub-fandoms) graduated and became recurring characters. In their place is a league of hip, young freshman replacements which suspiciously resemble the first generation of glee clubbers;
Mary Rose is just like the original Rachel Berry; Heterosexual, caucasian, skinny, pale brunette with a wailing Broadway voice is made the captain and lead singer of the New Directions. She also has a crush on a member of the football team who seems to be completely out of her league and is dating a nasty blonde cheerleader who hates her, which causes ominous wangst . Not to mention how despite her being unpopular the football player has a strange affinity for her, and how Rachel is the main protagonist season 1-3, whilst Marley is the main protagonist in season 4.
Kitty Wylde and Quinn Fabray's similarities are even lampshaded in the series; They're both (for at least a brief time) head cheerleaders, both caucasian, heterosexual and blonde with a strange, inconceivable hatred for the main heroine (see above) who has never done anything to them. They are both popular but implied that their "friends" don't really like them (Quinn's falling out with Santana/Kitty saying she really just wants friends). They're also dating the football player as a obvious Romantic False Lead, but seem to be using them for popularity at the best of times and get jealous and possessive over them even talking to other females in a purely platonic sense. It isn't helped by the fact that Kitty worships Quinn and constantly gushes about how she wants to be just like her. Or the fact that Sue dubs Kitty "A young Quinn Fabray, except not pregnant, manically depressed and in/out of a wheelchair", which crossed the Dude, Not Funny! territory for some viewers with experiences of that nature. They both have high, wispy voices too.
They don't even try and hide the similarities between Puck and Jake; Both from a broken home in which they didn't know their father, they both play/ed for the football team and have a big reputation as trouble makers and womanizers (To the point where Unique feels it necessary to break into a improv Britney Spears number to prove it). They both have strong, baritone voices and start off dissing the glee club and disputing it, before slowing warming up to the idea of singing and dancing on stage. They both are implied to see themselves as losers and both have a below average IQ and are popular. Oh yeah, and They're half brother. This is later deconstructed when Jake says he doesn't just want to be seen as a failure because his brother was, and that there's more to him than his genes. He's having a tough time it proving, though.
Unique/Wade is a big fan of both Kurt and Mercedes, so it's a good job the fandom refers to her as their lovechild from the future. When it comes to Unique being like Mercedes, they share body-shape and race, as well as having "Big belter" Whitney-esque voices and their main superlative being "Sassy diva". And being The Lancer to the main heroine of the series (Rachel/Marley). They both campaign for more solos throughout their airtime too, often claiming that their voices are neglected. When it comes to Unique being like Kurt, they have both suffered prejudice and bullying over their sexual orientations (Kurt is gay and Unique is transgendered), as well as auditioning for a big role in the annual Mckinley musical and for some reason or another not getting to do it. They also act as a Pet Homosexual to Rachel/Marley. They both show explicit interest in fashion and style, and are quite eloquently spoken for teenagers.
In House of Anubis KT came in after Nina had left (as Nathalia quit to focus on school work.) Many fans had this reaction at first, considering both of them are from the United States, were raised by a grandparent, and have a destiny to do with Ancient Egyptian Mythology. Some of the characters even seemed to believe this at first.
Loren's sister Olive disappears between seasons without any explanation. In her place, his sister-in-law Dorothy (whom he was courting before she ran off with another man, leaving him to marry her sister) came to town, fleeing the abusive husband she had ditched Lauren for, and taking Olive's place as Dr. Quinn's friend and confidant.
The third season introduced an annoying gang of German foosball players led by a man named Juergen. When the group reappeared in Season 4, Juergen was replaced by his previously-unseen brother Reinhold, presumably because the creators couldn't get Nick Kroll to reprise his role.
After Chevy Chase left the show, they introduced Professor Buzz Hickey, a Grumpy Old Man who has been at Greendale for a much longer time than the rest of the group, a Jerk with a Heart of Gold, a bit of an outsider and sort of a mentor to Jeff. He even takes Pierce's seat at the study room table.
Agent Antoine Triplett, who joins Coulson's team as a Sixth Ranger right around the time that Grant Ward is revealed to be a HYDRA agent. Both Ward and Triplett are badass, manly agents (compared to the meek Fitz and Team Dad Coulson) who previously trained under John Garrett and serve as potential Romantic False Leads for Fitz-Simmons.
Originally Pauline for Elaine, though since Pauline has run for three seasons now she has a rather well developed, unique character.
Morwena is very much one for Pauline though.
Averted with the replacement for Aunt Joan, Martin's Aunt Ruth is a very different person.
When the anonymous black sheepdog disappears, Joan gets a dog that takes just as much an unwelcome liking to Martin.
In Blue Bloods Danny Reagan's partner Jackie Curatola left the series a third of the way into season three due to actress Jennifer Esposito's illness. Danny had two partners that each lasted about five episodes each before finally ending up with Maria Baez as Jackie's permanent replacement. Both characters are Latina detectives from rough backgrounds, and with similar temperaments.
In Monarch of the Glen, the character of Paul Bowman was introduced in Season 4, and subsequently revealed to be the illegitimate half-brother of the main character, Archie MacDonald, Laird of Glenbogle. Two seasons later, Archie gets Put on a Bus to New Zealand, Paul Bowman-MacDonald is made the new laird, and the series carries on as before, including Paul having UST with Archie's wife. (Although it doesn't go anywhere.)
In Welcome Back, Kotter, as John Travolta—who played Vinnie Barbarino—became a celebrity, he left the show (returning every so often as a "special guest star"). His "replacement" was Steven Shortridge as Beau, a transfer student from New Orleans. Although Beau was as arguably pretty as Vinnie, Beau (as might be expected for a "replacement") never created the stir that Vinnie did.
After Ian Hendry quit his leading role as Dr. David Keel in The Avengers after one season, the producers were left with a number of leftover scripts. Rather than retool them, a new character named Dr. Martin King was created for several of them, while others simply had the name "David Keel" crossed out and "Cathy Gale" pencilled in, creating a rare gender-swap substitute and setting Cathy up to become iconic.
Downton Abbey, particularly in later seasons, seems to run on this trope:
After William is killed in World War I, Season 3 brings us Alfred: tall, fair-haired, awkward, and a potential love interest for Daisy.
It takes a while to determine who fits this role most closely, but by the end of Series 4, it appears that Charles Blake is turning out to be this regarding Matthew. He and Mary start out with an initially hostile relationship, then share a sweeter moment or two, and by the end of the season wants to marry her. Sound familiar?
Sarah Bunting has strong opinions, particularly where politics and class are concerned, likes helping people, and is attracted to Tom, much like the late Sybil.
Citizen Khan's first series had a red-headed mosque manager named Dave who converted to Islam later in life. In Series 2, he's replaced by a red-headed mosque manager named Dave who converted to Islam later in life. These are distinct characters, not an example of The Other Darrin. One suspects that the writers had Series 2 almost completed when Kris Marshall decided to leave and and only added a few lines introducing Matthew Cottle's version of Dave into Series 2 first episode to avoid having to go back and make more extensive changes.
On Two and a Half Men, Clark Duke looks so much like a younger Angus T. Jones that a casual observer might think they are brothers. In fact, in one episode everyone, even Alan, confuses Walden's new intern Barry for Jake.
On The Thin Blue Line Kray was replaced with Boyle for series two. The general opinion is that Boyle was a lot funnier.
Series 3 of Being Human ended with Mitchell, a vampire who was trying to leave a violent past behind him by refusing to drink blood and befriending a werewolf and a ghost, being Killed Off for Real. Series 4 then introduced Hal... a vampire who was trying to leave a violent past behind him by refusing to drink blood and befriending a werewolf and a ghost.
Silent Witness replaced Harry (handsome, cocky, quick-witted, plenty of UST with Nikki) with Jack Hodgson (handsome, cocky, quick-witted, plenty of UST with Nikki.) Jack did have the differentiation of being Irish and having his sideline as a cage-fighter worked into the storyline.
The Sopranos killed off the character of Richie Aprile in the last episode of the second season. In the second episode of the third season Ralphie is introduced. Although you could never mistake them for each other, they occupy very similar places in the show's universe; he even ends up dating Janice.