Two of the most-seen recurring villains in the first season, the Raiders and the Home Guard. The Raiders' lack of presence is due to a number of major defeats they suffered in the same episode where the Shadows are seen for the first time, though they begin to appear again later on. The Home Guard get one mention in season 2 before not being seen or referred to again, although former members show up in a group of pro-President partisans during the Earth civil war.
Despite being credited as a regular, Na'Toth in the first season appears in only five episodes, usually quite prominently. In the second season, thanks to a new actress with a noticeably softer voice, she appears only twice, gets a handful of lines, and disappears for the rest of the series (except a guest appearance in the last season, played by the original actress). She's credited as a regular for the entire season, though.
It's hard to know where to categorize Warren Keffer, a character created at the insistence of the network (they wanted a hotshot pilot/Han Solo-esque character) very much against the wishes of J. Michael Straczynski. He did create the character, and in his first outing, made sure to make him a prominent part of the episode. After that, he was seen rarely, only turning up in five more episodes, usually as a cameo. He was killed in the season finale. So, in effect, he was demoted to extra just as he was being made a character.
To a lesser degree, Lou Welch, one of the low-ranking security guards on the station, gradually disappears in season 2 as Zack Allen begins to get more and more screen time.
Leoben, in the last half season of Battlestar Galactica. He wasn't even used when they needed background Cylons. A deleted scene does imply only one Leoben remained after the civil war began, but it's never stated directly in either cut material or in on-screen canon.
He does get a larger role in The Plan, the feature length episode produced after the main series had finished. It was, however, set before the end of season 2, so quite what happened to Leoben (and the other Twos) is never addressed.
Beat the Clock is a rare example of both Ascended Extra and Demoted to Extra. The 1970s version was originally hosted by Jack Narz, with Gene Wood as announcer; Narz stepped down, with Wood taking over as host and Nick Holenreich announcing. A later revival from 1979 to 1980 had Narz as the announcer and Monty Hall as host.
During the first season of Beverly Hills 90210, Scott Scanlon is David Silvers' best friend. As David becomes accepted by Brandon and Brenda's friends, Scott is pushed into the background since he doesn't fit in with that group. He eventually develops a liking for country music and accidentally kills himself in front of David while playing with his father's gun in a second-season episode.
Leslie Winkle showed up three times in the first season of The Big Bang Theory, and her character was liked enough that the production team announced her as becoming a regular early in the second season. After about four episodes in, they quickly realized that she worked largely because she was a staunch, stubborn Arch-Enemy to Sheldon with no real room for her own stories or even Character Development. They quietly put her character aside and she shows up more sporadically since.
During the final season of The Bob Newhart Show, there are several episodes where Newhart himself has only one scene, which is not shared with any other characters (allowing him to perform one of his trademark one-sided telephone conversations).
Giulia Farnese barely even appears in Season 3 of The Borgias.
On Community John Oliver's character, Prof. Ian Duncan was initially featured in early promotional material as the main professor character in the show, but after a handful of episodes has essentially disappeared, with Senor Chang (Ken Jeong) essentially taking his place. Oliver did return in the first season finale, and took over as replacement anthropology professor in the next season. Despite being featured more than he was in the first season, he only turns up in a handful of Season 2 episodes. The showrunners wanted him to appear more, but Oliver was unwilling to move to California (where the show is filmed) due to his obligations to The Daily Show in New York, so his part was pared down. He makes a full return in season 5 as part of the Save Greendale Committee, even getting his own tag.
Jorja Fox on CSI: Sara left, then came back, but though she's credited as a regular, she doesn't appear in every single episode.
Deal or No Deal: The 25 models were the main attraction of the game show, but when the show entered syndication and the prize money was reduced, all but two of the models were replaced with contestants hoping their number would be picked so they can play the game, and if not, the contestants would open the cases during the game. The two models used in this version were for only spinning the wheel to see who can play and removing cases that were picked.
Happened to a lot of characters on Degrassi: The Next Generation, because the show has Loads and Loads of Characters (and they can only focus on so many of them). The most notable example would probably have to be Toby Issacs. He was a major character in the first 2 seasons. Come season 3, he became more of a background character and his screen time was significantly reduced (only getting a total of two major story lines from seasons 3-7 while it seemed like some characters would have a new story line every other episode). He was even removed from the opening credits during his final 2 seasons, before being Put on a Bus for good in season 8.
In the old days, past companions usually seemed not to exist anymore, even when they'd travelled with the Doctor for a long time, or taken part in important events. The Russell T Davies era made a point of avoiding this, allowing departed companions (like Martha, Jack, Sarah Jane and Rose) to show up again when they ought to.
Roger Delgado's incarnation of the Master. In his first season of Doctor Who, the character turned up in every single serial, from Terror of the Autons to The Daemons. Then, Delgado, while enjoying the show, became concerned that while officially a guest star, many casting directors considered him a de facto regular cast member of Doctor Who and therefore unavailable for other work. So in the next season dramatically scaled back his appearances, with an eye to making a splashy departure the following season. Due to his untimely death in Turkey, the character was quietly retired for a time.
UNIT appeared in almost every story for three seasons, then appeared in fewer and fewer stories after the Doctor gained space travel back - featuring as main characters in 2/5 stories in Seasons 10, 11 and 13 and 1/5 stories in Season 12. The most minor UNIT companion, Mike Yates, got officially kicked out after "Invasion of the Dinosaurs" but turned up for "Planet of the Spiders" in what was his last appearance. The Brigadier was dropped as a regular after "Terror of the Zygons", reappearing in a handful more stories in a cameo capacity ("Mawdryn Undead", "The Five Doctors", "Battlefield" and "Death in Heaven").
Harry Sullivan is a companion for Season 12 and then is dropped in "Terror of the Zygons", then appearing in a part amounting to barely more than a cameo in "The Android Invasion". The same cameo also involved UNIT companion Sergeant Benton's final appearance.
Christina Martinez is in the main cast of The Event, yet we barely ever seen her.
Ray's friends were much more important in early seasons of Everybody Loves Raymond, eventually showing up less and less.
Some of his friends were written out of the show entirely, such as Dave (played by Dave Attell).
Family Matters: The character of Judy Winslow, especially in Season 3 until she was eliminated without explanation completely in Season 4; she usually appeared only in scenes involving the entire family or to move a plot along. To a lesser extent, this also happened with Rachel Crawford (Thelma Hopkins, who was involved with other projects), despite making several bit appearances from Season 6 onward.
The show has a terrible habit of promoting recurring characters to the opening titles, but then giving them less to do, or simply giving less to regulars with each passing season. Among them:
Jaime "Kingslayer" Lannister appeared in only four episodes of Season 2, but was billed third for all of them. This was due to his being a prisoner of the Starks. Once he was free, he became a dominant character in Seasons 3 and 4.
Petyr "Littlefinger" Baelish was a very major part of Season 1, and appropriately billed as a regular for it. He was also billed as a regular for the following seasons, despite appearing in fewer episodes each season.
Theon Greyjoy, after being a pretty major part of Seasons 1 and 2, spent all of Season 3 basically just being tortured, and only appeared three times in Season 4.
The characters of Varys, Lord Commander Mormont, Ramsay and Gilly are glaring examples of characters added to the opening titles only to appear in fewer episodes than previous seasons when they were just guest stars. They, along with a few others, appeared in fewer episodes than characters who still were credited as guest stars.
The Dothraki were important enough to have a Con Lang in Seasons 1 and 2, but are reduced to the background in Season 3 and are largely invisible in Season 4. In season 5 they vanished entirely.
In contrast to being a major viewpoint in the books, Catelyn increasingly becomes a supporting character to Robb's Adaptation Expansion romance with Talisa, particularly in Season 3.
Tommen and Myrcella were demoted in early seasons (including extended absences after Season 2) but appear to be ascending in later seasons with Tommen recast for Season 4 and Myrcella recast for Season 5.
The secondary characters of the Kingsguard are mostly rolled into the Composite Character Meryn Trant. Bronn even lampshades this when he refers to one of them as "Ser Whosit of Whocares?"
Except for Loras and Brienne, Renly's Kingsguard is the same. This is most evident when Brienne is totally unfazed by killing two of them, an act that haunts the doer in the novels. Their names were Emmon Cuy and Robar Royce, incidentally.
Ser Dontos Hollard plays a much more prominent role in Sansa's storyline in the second and third books than he does in the same period of the series.
In "Blackwater", the extra who acts as Stannis' number two aboard his flagship is credited as Ser Imry Florent, the admiral who led Stannis' fleet into Tyrion's trap in the novels.
Subverted with Stannis' wife Selyse, who is portrayed by an extra in "The North Remembers" and promptly forgotten, but becomes an actual part of the cast in Season 3.
House Greyjoy plays a more negligible role in the War of Five Kings, particularly after the Sack of Winterfell. For instance, Robb's first priority in the novels after the Battle of Blackwater was to drive the Greyjoys out of the North rather than to besiege Casterly Rock.
House Tyrell's importance drops off exponentially in the second half of Season 4. After Margaery's midnight visit to Tommen's bedchamber, the entire family is reduced to background characters for the rest of the season. Loras Tyrell in particular has only a few lines in "The Lion and the Rose" even before that.
Jared Padelicki spent most of the start of the fifth season closing out Dean Forester's arc, which acted mainly as a promotional vehicle to keep him in the running for a show on the network the next season known as Supernatural.
After Richie Cunningham left, his friend Potsie remained on the show in various different roles before getting a job working for Mr. Cunningham. His screen time, however, was greatly reduced and he wasn't present in several episodes because the writers struggled to find things for him to do.
Also poor Lori-Beth, who is a minor recurring character who later becomes Richie's steady girl. When Richie left, she stuck around, getting married to him over the phone, and giving birth to Richie's son when he was away. Eventually, she just stopped appearing entirely unless it was a special occasion, having little way to play off the others.
Micah in Season 3 of Heroes. He goes from being a series regular to only appearing in a few episodes of Season 3 after his storyline was dumped from most of the show.
Since Heroes has Loads and Loads of Characters, every single series has demoted at least one of them to extra so far. And completely written out a couple of others.
The Haitian in particular suffered badly from this. Never a prominent character, by the final season most of his appearances were reduced to a single scene every few episodes. On at least one occasion he didn't even get a line - rather, he simply stood in the background to imply that the good guys would use his power in some way (not that they ever actually showed it happening).
Kay Howard on Homicide after her promotion to Sergeant, especially in Season 5 where she does nothing until the season finale, after which she's Put on a Bus. To a lesser extent, Munch from Season 4-on and Bayliss for most of Season 7.
On House, Doctors Cameron and Chase were fired from the title character's team at the end of Season 3. In Season 4 they were shown to have taken new jobs at the hospital, while House recruited a new team.
Season 6 has a lot of demotions: Cameron becomes a long-distance extra, while Chase found his way back into the cast.
Christina Gallagher has a fairly prominent role as Peter Russo's girlfriend/assistant in Season 1. In Season 2, she's kept around by becoming Chief of Staff Linda Vasquez's assistant, but with no real arc besides Claire briefly using her to manipulate the First Lady and strain Walker's marriage. After Frank manipulates Linda into resigning, Christina is very quietly transferred out.
The head of the Underwoods' Secret Service detail, Edward Meechum, had a subplot in Season 2, is largely reduced to silently escorting people around in Season 3. He is given a little bit more to do in season 4, and then is promptly killed off a third of the way through the season when he's shot by Lucas Goodwin in an assassination attempt on Frank.
Since Season 4 of iCarly started, Freddie's mom Mrs. Benson, was used sparingly. It's possible that Gibby being promoted to the main cast is the reason for this.
Once Yutaka Ishinabe, Roksaburo Michiba, and Koumei Nakamura retired from their positions as Iron Chefs, they were demoted to extras, only appearing for specials.
JAG: Andrea Parker was the female lead in the Pilot Movie, but wasn’t liked by the network so she was only a recurring character in a few first season episodes and in one season six episode.
In Kamen Rider Kiva, Basshaa is the only character to not get a specific arc, and never gets a Fever attack when Kiva upgrades to Emperor form. In the next series, Kamen Rider Decade, Basshaa gets his ass blown away effortlessly in each fight—in the second, he doesn't even get a single shot off!
Jack McCoy on Law & Order after getting promoted to DA. Interestingly, this was at Sam Waterston's request—when Fred Dalton Thompson left, Waterston campaigned pretty hard for McCoy to get the promotion.
While it was understandable that Captain Deakins of Law & Order: Criminal Intent was not used as heavily as other Captains/Lieutenants in the Law & Order universe (as his actor, Jamey Sheridan, lived on the West Coast while all the scenes were filmed in New York and he eventually left the series due to stress of traveling and health issues), ADA Ron Carver gets this trope pretty badly. Within the first four seasons, he worked alongside Goren and Eames as the competent and by-the-book (if not underused) "Order" side to coincide with the "Law" aspect of the series. However, gradually within season four, namely with the return of Detective Mike Logan, he would share a scene or two with whichever detective team was in that particular episode just to inform them of what they legally can't do in a case and offer a suspect a deal before being written off the show without a clear reason. Even on This Very Wiki underneath CI's character page, both characters' profiles have been mysteriously deleted.
In the first half of the first season Eliot Stabler's four children were regular characters, however after that they became infrequent recurrers showing up about once season. Two of his daughters have not even been seen since the seventh season and between that and the first they had about 3 appearances each. This oldest son (who is the twin of one of the daughters) has remained showing up about once a year and later had A Day in the Limelight, and his middle daughter had a subplot about her being a bipolar thieving drug addict.
The entire rest of the supporting cast has fallen victim to this. Most noticeably are Munch, Fin, and Huang, who used to get entire subplots in every episode and now don't even appear in half of them. Cragen might have a scene or two, and Liz might have a line per episode. Nowhere near the screentime of Stabler, Benson, and the ADA (Alex, Casey, or whoever the rotating one may be).
The Lawrence Welk Show: The legendary bandleader always liked to spotlight many of his new stars of his orchestra during a given show, giving them solos. Legend has it that Welk used this as a probation period for his new stars, and used audience reaction (both in-studio and viewer mail) to determine if the band member was worth keeping. If they were, they were featured more prominently ... and sometimes, even given longer solos. If not, ... well, the unlucky band member – regardless of his actual talent – began fitting the trope before being fired.
Unfortunately, possibly due to budget from the TV show, not all off The Letter People got to be seen much and few such as Mister Z and Mister V were Put on a Bus. In the Classroom version, they appeared more and you were allowed to use a Letter Person or more into a story or lesson as much as you desired. The same happened with the Word Machine. In the TV Show, he only appeared in one episode and was invented by Professor Foghorn. In the classroom version, we don't really know where the Word Machine came from, but he appeared more then just one story and he needed the Letter People to help him make words rather then just simple letters like in the TV show. Plus, alot of the Letter People got involved in the Runaway words mishap then just Miss O.
Carrie Ingalls on Little House on the Prairie, who went from a major character in the first four seasons, to walking scenery during the next four. She was lucky to get a line once an episode... then once a month... then once a season.
Though still listed as a main cast member, Desmond was commuting on a bus to make brief appearances in a few episodes in the fifth season. Still listed as a main cast member (on the episodes, not in the press releases) in season six... he showed up in the first episode, but didn't show up again until the second half of the season.
Frank Lapidus was also Demoted To Extra. He was a pretty major character during Season 4 and most of 5, but when Season 6 came around he seemed to have gotten lost in the shuffle and became an extra body and frequent cheesy One-Liner. Pretty ironic considering Jeff Fahey wasn't promoted to the main cast until Season 6. Made worse by the fact that we never really knew who Lapidus really was or where he came from, as he was one of the few main characters to never get his own flashback episode. The one flashback he did get was in an episode that he shared with several others, and all it did was explain how he got onto the freighter that came to the island.
Happened to Rene David in Season 2 of The Lunchroom. Despite being Will's love interest and the closest thing to a female lead the show had in the first season, she only has a few minors scenes before disappearing without explanation.
In Seasons 1-5 of The L Word, Kit was one of the main characters. In Season 6, she existed primarily to say "Girl!" about once per scene. After two seasons of being a core member of the cast, Jodi also fell into the background during Season 6.
Kristen Prout (Char) was demoted to recurring status on The Lying Game. Sharon Pierre-Louis (Nisha) was also demoted but she had never really been a major character in the first place. Neither appeared at all in the second season.
After Katey Segal's tragic miscarriage on Married... with Children, where the producers had written her pregnancy into the storyline before being being forced to backtrack, the character of Peg Bundy was instead subjected to this trope during the second and third times Segal became pregnant during the show's run. Both times, Peggy was sent out in search of her missing father, and was only shown in voiceovers talking to her family on the telephone, or only shown in scenes where she didn't have to do anything strenuous and the viewers couldn't see her pregnancy. Happily, Segal's later two pregnancies were both successful, and when she was ready to return to work the producers brought Peggy home, much to Al's chagrin.
When M*A*S*H made it to the little screen, several characters from the movie had this happen to them (when they weren't eliminated entirely): Spearchucker, Ugly John, and Lieutenant Dish were all reduced to second-tier status, and all were gone from the show well before the end of the first season. The character of Spearchucker was supposedly written out for greater historical accuracy, as the writers claimed there was no record of African-American surgeons serving in Korea. (There were, in fact, black doctors in Korea, and Spearchucker was based on an African-American doctor Richard Hornberger heard about at the 8055.)
Especially in Season One, the show had a habit of taking the names of reasonably significant Arthurian characters, like Pellinore, and giving them to random knights, who were then killed.
In series four and five, Gaius is given virtually nothing to do except provide exposition and exist as a sounding board to Merlin. True, that was always his role, but he was also given several character-centric episodes in the past. This was not necessarily a bad thing, as the introduction of the knights of the Round Table at the end of series three meant that the show was juggling Loads and Loads of Characters, and one of the themes of the season was passing on the torch to the younger generation.
Gwaine became this in series four and five - oddly enough, he got more screen-time and characterization as a guest star than as a series regular.
Bob was a regular for the first season or so of The Middle, but after the show began to focus more on the Hecks' lives and less on Frankie's job, he had little use on the show and was relegated to the end credits.
Bob in series two, where the lack of a zoo setting gave him no real reason for being around. He gets a bit better in series three where he becomes the owner of the club the Boosh frequent, but only slightly.
In the radio version of "Mutants" Joey Moose adventures alongside Vince and Howard throughout it and proves to be a competent ally, while in the television version he's killed in the opening scene and his body parts are used to make the mutants.
This started happening to Kimberly in season three of Mighty Morphin' Power Rangers. Notably, she was the only one who didn't go to Edenoi during the season premiere (AKA the Poorly Disguised Pilot for Saban's Masked Rider) due to a cold (though she made use of reduced screentime awesomely, being the only Ranger left on Earth when Rita and Zedd sent a new Monster of the Week), and had her powers drained halfway through after being captured by Kat Hillard. Since Amy Jo Johnson actually told Saban she was going to quit beforehand, instead of clumsy camera tricks and an abrupt Fake Shemp, half the season was spent slowly easing her character out of the Pink Ranger position and setting up her successor.
Bulk and Skull start getting less screen time as time went on. First in Turbo they were turned into chimps for a good portion of the series. It wasn't until In Space that their screen time was cut significantly due to the focus being on space travel and the rangers having little time on Earth. Aside from one small cameo, the duo are mostly absent through the series middle episodes with the bulk (no pun intended) being at the beginning and end of the series.
After Skull was Put on a Bus in Power Rangers Lost Galaxy, the writers apparently had trouble coming up with material for Bulk on his own. He only appears in a few episodes (he does get last billing in the title sequence in those episodes though). He would not have a recurring role again until Power Rangers Samurai 12 years later.
In Power Rangers S.P.D., Sam the Omega Ranger was demoted compared to his counterpart DekaBreak from the source material. Disney forced a Fake Shemp situation that the writers didn't want to deal with, and they wouldn't have included Omega Ranger at all if they weren't stuck with so much DekaBreak Stock Footage.
Mindy's best friend Gwen was a series regular at the beginning of The Mindy Project, but only appeared in the occasional episode before being written out entirely. Danny also had increasingly sporadic appearances throughout season 4.
Steven Hill was originally the main star of Mission: Impossible, but partway through the first season (after, among other things, his returning to his roots of Orthodox Judaism meant that he refused to work after sundown on Fridays) he was downgraded to only appearing in a couple scenes per episode. And then he became the first - but not the last - member of the IM Force to fall victim to Chuck Cunningham Syndrome.
Following Richard Hunt's death, Scooter was used far less often - not appearing in most productions and having minimal screentime in others. The 2011 movie appears to reverse this. During the 1990s, he was damn near unpersoned. Other characters without performers (like Rowlf, Dr. Teeth and Janice) at least made token unspeaking cameos, but Scooter was nowhere to be seen for just shy of a full decade.
In the 1960's, Rowlf was pretty much the main star and leader of the Muppets, with Kermit being more of a second-tier character. In the 1970's, when Kermit officially became a frog and his personality was fully-realized, Rowlf turned those leadership duties over to the frog and became more of a secondary character, yet he remained a prominent character in Muppet productions. After Jim Henson's death, his appearances became limited to mostly brief non-speaking background cameos. When Bill Barretta started performing the character, he gradually returned to regular speaking roles and core character status.
In the Sex and Violence pilot the show was hosted by Nigel. When The Muppet Show became a series, Nigel's role was that of the orchestra conductor, and while he was seen fairly often in all five seasons, on the show he only had dialogue in three episodes total, all from the first season.
Dr. Teeth and the Electric Mayhem, throughout the '90s - with only Animal maintaining a steady presence and involvement in stories. Likely a result of Jim Henson and Richard Hunt's passings.
Beauregard used to be a prominent character on the show, movies and TV specials, but fell out of use because the scriptwriters, while liking him as a character, had problems with finding material for him. (The problem, according to one of them, was that Beuregard "has no desires; he doesn't want anything.") Nowadays, you're lucky to find someone who remembers him. note His last major role was in The Muppets Visit Walt Disney World, a special that's been rarely seen since is initial broadcast due to Jim Henson's death ten days after its premiere. In the special, he's paired with Miss Piggy, tricking her into riding thrill rides instead of shopping and dining. This gets a reference in the 2011 movie, where he's spent all the time since the group had a regular show in the theater wondering where everybody went.
If your familiarity with the Muppets is only with the movies, it comes as a surprise to see what a major character Link Hogthrob was on the Muppet Show proper. He only had cameos in the films (he has a very brief speaking role in The Muppets Take Manhattan, and then is reduced to background character until an equally brief role in Muppets Most Wanted).
Dr. Julius Strangepork didn't appear much on the show outside of PIGS ... IN ... SPAAAACE! anyway but has made a few background cameos here and there.
Bean Bunny after the early 1990's.
Clifford was the last Muppet designed by Jim Henson and it seems they had something planned for this guy. But after Muppets Tonight went off the air...
Johnny Fiama and Sal Minella, after 2005. In fact, most characters created for Tonight disappeared entirely once the show was cancelled; Johnny, Sal and Breakout Character Pepe are notable for sticking around at all.
Giselle in Season 1 of The Next Step, after being brought down to B-Troupe. Eventually the same thing happens to both Tiffany & Stephanie as of Season 2.
Towards the end of Night and Day, Will appears to take on a much reduced role – often appearing in a background or supporting capacity – until he’s unceremoniously killed off when, during an argument with her virginity fairy (don’t ask), Kate accidentally drops the Complete Works of Shakespeare on his head.
Brian in The Nine Lives of Chloe King. In the books Brian knew that Chloe was a Mai, and was a member of the order trying to kill her. He also didn't die in the books.
Jimmy Cooper as of season two of The O.C. Tate Donnovan still received an And Starring in the opening credits, but Jimmy didn't really do anything other than hang out on his boat.
Two of the poker buddies, Vinnie and "Speed", appeared in less and less episodes in later seasons of The Odd Couple.
As Once Upon a Time kept introducing more characters from outside Storybrooke, everyone who wasn't part of the Snow-Charming family started getting reduced to cameos. This gets a Lampshade Hanging in season 5: Leroy/Grumpy says the dwarfs will join the quest to Camelot because they're tired of not being involved in things. They proceed to get written completely into the background of the Camelot storyline.
Following Episode Three of The Pacific, Colonel Lewis Puller makes a sole appearance when the 1st Marines is relieved by the 5th after the disastrous attack at Bloody Nose Ridge.
In the seventh series of Red Dwarf, Arnold Rimmer only appeared in person in two episodes, then was relegated to flashbacks, dream sequences and—in one memorable case—a theme park ride based on his own diaries. The actor playing him, Chris Barrie, had decided to leave the show and had a very limited schedule, so he agreed to appear in a handful of episodes (and sequences that could be filmed out of order, such as ADR or flashbacks).
In Robin Hood both Much and Allan-a-Dale, who were hugely important characters in seasons one and two, ended up being lucky if they got three lines each in season three. They were shunted aside in favor of Kate.
Serial-specific example in The Sarah Jane Adventures episode Whatever Happened To Sarah Jane: Clyde gets about three minutes of screentime in part one, and is a background character in part 2. In addition, due to being Ret Gone, Sarah Jane is only seen sparsely throughout the serial, Luke only appears at the beginning and end of the story, and Mr Smith only appears at the end of episode 2.
Happened to Yvonne Hudson. She was fired along with most of the ill-fated 1980-81 cast, but hung around as an extra until 1984.
Ever since season 32 note 2006-2007 season, Seth Meyers hasn't been in any sketch outside of Weekend Update, possibly due to becoming a head writer. He has appeared in some sketches (like in the "Original Kings of Catchphrase Comedy" pretaped sketches as Boston Powers note A comedian who dresses and talks like Mike Myers' Austin Powers character), but it's rare.
In universe in SCTV, after Johnny LaRue's crane shot from a made for TV movie causes the station to go over budget.
The Secret Circle. Nick was Cassie's love interest in the books. In the series he is quickly killed off and replaced by his older brother Jake (who wasn't in the books).
Jane was also prominent in the first nine episodes. Since then, she's only appeared a couple of times before getting killed off like Nick.
Though he isn't a huge character in the book, Mr. Palmer is only briefly featured in one scene of the 1971 Sense and Sensibility Mini-series - the ball where the Palmers are first introduced - and is never seen again. Therefore, we get none of the character development from the novel when the Dashwoods become better acquainted him during their stay at Cleveland.
Forgetful Jones has not been given any prominent roles on Sesame Street since 1992, but has made recent nonspeaking background appearances. The character's initial retirement was due out of respect for Hunt's death.
In Sharpe, because the TV version of Sharpe's Rifles introduces Teresa early, Major Blas Vivar's role is downplayed in her favor. In the books, Teresa debuts in Sharpe's Gold.
In Series 3 of Sherlock, the main focus is how John and Mary's marriage has changed the dynamic of the show. Lestrade's still in all the episodes but he doesn't do that much plotwise.
Roger was seen far less often in Season 5 of Sister Sister. Marques Houston was part of development for a new show (which never got picked up), but he also took time off because of his mother being diagnosed with cancer.
Starting in Season 14, Danny Bonaduce, Leif Garrett, Frank Stallone, and Tonya Harding have been featured less and less, to the point that one or more of them may only get in one comment/joke during the entire hour.
In universe example on Sons of Anarchy: Rane Quinn went from being the president of the Nomads charter to being a low ranking member in Indian Hills, a chapter that's only been around for two years and was started via patch over.
In season 2, Sandra Benes went from being one of the senior staff to barely having any lines when she appeared. That is, if she was even supposed to be the same character. Oddly, she was called Sahn during season 2. Her original role seemed to be given to another Asian character named Yasko.
Castus was historically the German general of Spartacus' rebellion. Here he's a guy who's seems to be causing problems to the Nagron ship. Granted, this demotion may be because Agron was already given his supposed role and characterization for much of the series. The show-runners milked those two's interactions for what it's worth.
Arrius was historically the one who defeatedCrixus. Here, he is portrayed as an Elite MookGeneral Ripper whom the latter killed instead.
Like Arrius, Commander Rufus was historically part of the forces that defeated, if not killed, Gannicus and Castus (Agron). Here, he is Crassus' Mook Lieutenant.
Cindy Makey on Spooksville. In the books, she was one of the main characters, but in this series, she's only been a one-shot character so far.
Ever since ESPN and the NHL parted ways, hockey highlights have now become few and far between on SportsCenter. According to Deadspin's weekly "Bristolmetrics" article, which breaks down the show's coverage of sports and athletes in terms of time spent on a subject, the NHL averages only 15-20 minutes of highlights per week during its season. The hardest hit were Gary Thorne, the chief hockey announcer during that time, and Barry Melrose, who left Bristol for a small time to become head coach of the Tampa Bay Lightning...that didn't last long.
Though Elliot, Kim, Chris, Dave and Will were always supporting players, they were usually allowed to participate in Aaron Sorkin's banter throughout each episode of Sports Night. Starting in Special Powers, and continuing through most of the season, they were relegated to bit player status, just saying things like, "Sound's up on 23."
Richard Dean Anderson's final season as a regular on SG-1 had him promoted to general where he had vastly reduced screen time.
Stargate Continuum opens with an over-the-shoulder shot of Pentagon liaison Major Davis walking down the corridors of Stargate Command. He was a fairly major recurring character in the earlier seasons of the TV series, so you might expect him to have at least one scene, but nope, the camera quickly cuts to the main characters, and all you see of Davis in the movie is the back of his head for several seconds. The director did this as a joke, according to the DVD commentary.
Teal'c is the only member of the original SG-1 who did not appear in Stargate Universe.
Meanwhile, of all the characters who survived the original movie, Feretti is the one the writers forget exists. In fact, despite dying in the first regular episode of SG-1, Kawalsky makes far more appearances than Feretti (Kawalsky gets Time Travel, Alternate Timelines, Parallel Universes, illusionary worlds. Feretti gets... one brief appearance in the first season finale, one mention in season three, and never, ever has his existence hinted at again.) Feretti's lack of appearance was initially attributed to the actor having other commitments, but SG-1 far outlived Brent Stait's role in Andromeda, and Brent Stait has even appeared in Stargate Atlantis as someone who was not Feretti. He's been treated much better by Fan Fic: the show's sheer lack of love for him kept him on the minds of enough fans that he's got plenty of fanwork dedicated to him.
On Stargate Atlantis Weir and Ford did this before being dropped entirely. Weir's actress could not return to do any more episodes (despite the writers having plans for a longer arc involving her), so they pulled (another) The Other Darrin on her (the character's 2nd time) before having her Put on a Bus. Ford just wasn't very interesting to them, so despite bringing him back several times he was eventually dropped.
As Seven of Nine got more focus on Star Trek: Voyager, Chakotay was one of the characters to lose it. Reportedly became a cause for complaint from his actor.
Dr. Vijay Kochar was a regular during season 1 and 2 of St. Elsewhere, only billed as a guest star thereafter.
Step by Step: The character of Brendan Lambert, the youngest son of family patriarch Frank Lambert, was given fewer plots and lines before being eliminated completely by the sixth season. To a lesser extent, this was also the case with Mark (the nerdy middle son of Carol Foster), although Mark would continue to appear sporadically until the series ended, usually given one-liners or in family scenes whereby his absence would be conspicuous. These reduced appearances were perhaps in part due to the shift in focus on the female siblings, especially one-time tomboy Al (after Christine Lakin grew in desirability as she became an adult); while many of the remaining stories were 5-year-old Lily (who was born in 1995 and was age-advanced to create "little girl" stories).
Guy Blank was part of the main cast in Season 1 of Strangers with Candy, and recurring in early Season 2 before being...
The fate of some of the professional dancers who weren't asked to partner celebrities in the 2010 series of Strictly Come Dancing; those who agreed were put into a "professional dance troupe". The following year the dance troupe was removed, although Ian Waite is apparently too popular to lose altogether as he still regularly appears on It Takes Two and occasionally partners celebrities in special charity or Christmas editions.
The Suite Life of Zack and Cody and The Suite Life on Deck: Maddie and Carey, who were part of the original main cast on the former show, appeared occasionally on the latter show, which switched the main setting from a Bostonian hotel to a high school on a cruise ship, justifying the demotion. Also, possibly a Justified Trope with Maddie, given her presumed age (being three years older than the boys) would make her a college student in the first season of On Deck.
The original version of Survivors did this with several characters as the focus of the show shifted from season to season. Jenny in particular started out as one of the principal characters, faded away almost completely, then came back to star in the third and final season.
Takeshi himself in most of the foreign dubs of Takeshi's Castle, to the extent that he practically qualifies as The Ghost. Since his main role was as narrator in the Japanese original though, this was kinda inevitable.
John Burns had a couple of episodes centered on him early on Taxi, but he became increasingly ignored, being written off after the show's first season. This was lamp shaded in his second-to-last episode ("Hollywood Calling") when John took a week off to study for his finals and practically no one seemed to notice.
In The Tomorrow People, the character of Tyso Boswell was introduced in season 3 with great fanfare, along with several quirks that allowed for strong character and story development (a close friendship with Stephen, claustrophobia, extra-sharp senses, a possible growing-up arc, his Romani backstory, etc). However, after Tyso's second serial World's Away, many of these facets were dropped. Come season 4, Tyso was only just saved from obscurity with the occasional line of dialogue. He was dropped from the series altogether at the end of that season, leaving fan fiction writers to fill in the blanks later on.
In latter half of season 1 of Total Divas, Jojo is barely featured at all.
Despite being a strong character in the third season of True Blood and central to the plot in the fourth, Holly Cleary's significance is quickly reduced from then on to simply being Andy's girlfriend. It is telling that she hasn't done anything magic-related since the fourth season.
Mathur, 24 (India)'s version of Jovan Myovic. Most of his duty is done by the unnamed counterpart of Jonathan Matijevic.
Johnny Horne, Audrey's brother, appears in a few early episodes of Twin Peaks before disappearing until a late season 2 cameo.
Jake, starting with Season 10, when he left to join the military and only appeared sporadically. Even before that, his role slowly started to diminish. By season 11, he has officially left the show entirely.
Evelyn only appeared in one episode in season 10, and four in season 11.
Judith started to become this in Season 9, although now she has officially been Put on a Bus.
With Charlie dead, it's very unlikely that Rose will ever play a major role in the series again, although it has been shown that she is now stalking Walden.
In season 3 of The Vampire Diaries, Katherine appears sporadically for the first half of the season, then takes off after Homecoming. Returns to a significantly more important role as of the second half of the fourth season.
In the comics, Donna was around for the first arc and a half before being killed.
Doctor Stevens played a vital role in the Woodbury arc in the comics, but only had a couple of scenes with a few lines on the show.
Very prevalent in the weird final season of Welcome Back, Kotter. Mr. Kotter only makes fleeting appearances, due to actor Gabe Kaplan not being very happy with the show. No one acted as though it were at all unusual that Mr. Kotter hardly seemed to be around any more. In fact, Gabe Kaplan still got top billing. At least Barbarino, who was also absent that season because John Travolta was doing movies, was explained away as having dropped out of school. To preserve some semblance of familiarity, the previously stay-at-home Mrs. Kotter became the Sweathogs' new adult supervisor in her role as the school secretary, or something.
Much of the main cast from the first 4 seasons were Demoted to Extra as the presidential race took precedence over the running of the White House in the latter seasons. Of particular note, perhaps, is Toby, who was summarily dismissed by the president, and appeared in less than half the episodes of the final season, and those for very small amounts of time (despite Richard Schiff being paid for all of them...).
Abbey Bartlet in Season 7, where she no longer appears in the opening titles unless she appears in the episode. She's also absent for quite a while in Season 5 as she is in New Hampshire, helping Zoe recover from her abduction and blaming Jed for Zoe being a target.
Jimmy McNulty in season four, going from being the defacto star in the first three seasons. Dominic West wanted some time off to do film and theater and spend time with his family, this was explained in series by McNulty deciding to leave the Major Crimes Unit after his adversary was killed before he could take him down, becoming a patrolman and mending his ways while he was at it. He got off the bus in season five, though.
In the fifth season, many of the supporting (and even major) characters from the previous seasons appear during several episodes of the series, largely as a reminder that life in Baltimore keeps on going, even when the major plot arcs end. Roland Prezbylewski, the other three main child characters from season four, Cutty Wise, Nick Sobotka, Bunny Colvin and several others show up in different scenes. More notably, however, various characters who were glimpsed in previous seasons also return, including Clay Davis' limo driver, several dock workers (who are now homeless) and former members of Avon Barksdale's gang who were prominent in the first and second seasons.
Similarly, since the fourth season dealt with the school system, this inevitably led to less focus being spent on the actual police force.
Wee-Bey after he's sent to prison. He does have some more screentime in season 4 due to one of the plotlines revolving around his son Namond.
Poot in season 5.
Beadie after season 2.
Namond Brice is a central character in season 4 but only appears briefly in one episode of season 5.
Tiana "Black Widow" Noguchi on WMAC Masters, despite the fact she was supposed to be the women's champion but she was never seen competing. Her brother Cyclone had it almost as bad but he was finally given a match in the last episode against The Machine. The two also barely used backstage.
Dustin barely appeared in the last two seasons of Zoey101.
With the second retool of 3-2-1 Contact in 1986, the seasons 2-4 cast was relegated to a few cameo appearances.
The last season of 3rd Rock from the Sun sees Tommy demoted to an occasionally recurring and not very important cast member, partially because he's off to college and thereby separated from the rest of the cast most of the time. The actors playing Nina and Don were listed as regular cast members starting on the third season, but likewise appeared only occasionally on the last season.
Josh Girard, who was prominent in season one as Jenna's male co-star, and reduced to an almost anonymous staff writer.
The 100th episode lampshades this with the new actor Danny having replaced Josh on the show-within-a-show as the "other guy", no explanation for Josh's complete departure is given, and everybody keeps forgetting Danny wasn't the "other guy" that was with them from the beginning (even Danny starts to mix himself and Josh up under the effects of the gas leak).
Josh actually reappears briefly before that, when he throws a fit over how he's been neglected and ignored and quits - then later, auditions for his own old job back and loses to Danny. Danny ends up befalling the same fate anyway.
Cerie Xerox in the last two seasons. This is explained near the very end of the series when the entire staff of TGS quits, and she reveals that she had actually quit two years prior. However, it's not explained why she continued to show up.
Maia on The 4400. She was one of the most prominent 4400's when the show began, but eventually her role was reduced to being Diana Skouris's daughter and morality pet, along with the occasional prophecy. This is likely due to a couple of reasons. One of which is the mysterious nature of the show, and as Maia's abilities became more powerful she would essentially be able to solve most of the shows big mysteries in minutes instead of over the course of several episodes. The second reason is child labor laws...