All My Children's Dimitri Marick first appeared onscreen rescuing heroine Natalie from a well where she'd been imprisoned by her psychotic sister Janet. As he tended to her, he repeatedly had flashbacks of a very similar appearing woman falling from a horse. Despite genuinely falling in love with Natalie it was very obvious that a huge part of his attraction to her was her resemblance to this mystery woman. Viewers soon learned that the woman was his wife and that she hadn't even been killed, just severely injured and left in a vegetative state.
In Season 5 Wesley's Love Interest 'Fred' Burkle is killed so her body can by used by Illyria. In exchange for Illyria agreeing not to kill anyone, Wesley acts as Illyria's guide to this strange new world she's been reborn into. Angel flat-out asks Wes if he's in love with Illyria; he denies it adding, "But I do need her." Wes does try to limit this trope — when Illyria offers to take Fred's form to understand human relationships Wes is outraged and refuses to speak to her for a while. Just before the Grand Finale, which no-one expects to survive, Team Angel spend their time doing simple things they enjoy. Wes on the other hand just tends to Illyria's wounds, and she once again offers to comfort him by taking Fred's form, but Wesley refuses because he knows Fred is gone and to accept anything else would be a lie. "And since I don't actually intend to die tonight, I won't accept a lie." When Wes receives a fatal wound, Illyria asks "Do you want me to lie to you now?" Wes agrees, and Illyria morphs into Fred, telling Wesley she loves him and that they'll be together in the afterlife.
The second Conduit is this to the first one.
Battlestar Galactica (1978): Lighthearted example: In the original show, the robotic-drone daggit ((AKA a dog)) replica Muffet II was created as a replacement for Boxey's pet daggit Muffet who was killed by falling debris during the attack on Caprica.
This is the origin of the Cylon Centurions. Replace a goldfish (namely your dead daughter), set in motion the end of your civilization.
Oh, and Cavil was made in the image of Ellen's father.
All the human models seem to be Ellen and Tigh's replacement children and/or the Final Five's replacement PEOPLE.
Being Human: This trope is discussed by name - and involving an actual goldfish - in one second series episode.
The Big Bang Theory: Raj becomes closer friends with Stewart, the local comic book shop owner, after his Heterosexual Life Partner Howard Wolowitz gets married and goes to space. At one point Sheldon even refers to him as "fake Wolowitz" and insists that if Stewart if is hanging around the group more now he has to act just like Wolowitz. It's worth noting, however, that Stewart is also a very lonely individual and was more than happy to be recognized as the replacement so long as he gets companionship out of it.
Black Mirror: In the episode Be Right Back there is a whole online service devoted to replacing loved ones with an online relationship. And if the client wishes it; to have a full replica of the person.
The Borgias: Has Ursula Bonadeo, Cesare's love interest. He meets Ursula while visibly distraught during his sister Lucrezia's wedding, and essentially transfers his obsession with Lucrezia to Ursula. They share the same hair color/clothing styles, and both suffer from abusive husbands. Fans love pointing out how many of Cesare's conversations and even poses with Ursula mimic his interactions with Lucrezia.
The Buffybot doesn't start out this way, but after Buffy dies at the end of Season 5, one of the series' more poignant scenes features Dawn, missing her big sister, lying down next to the Buffybot and cuddling with the robot as it charges. Furthermore, in the same episode we see Giles trying to instruct it in Eastern philosophy during a sparring session.
Well, it actually sort of did start out that way, since it was built by Warren to be Spike's Doppelgänger Replacement Love Interest for Buffy who rejected his advances. Ironically after Buffy's death Spike can't stand to look at the Buffybot, and is disgusted when it obeys its earlier programming and tries to flirt with him.
Caprica: By the series finale, Daniel and Amanda Graystone have fully accepted the Zoe avatar as a substitute for their dead daughter (it helps that she possesses almost every memory that the original Zoe did), even providing her with a physical body so she can interact with the real world.
Dark Angel: Max is eventually informed by her former commander and father figure, Donald Lydecker, who had been hunting her and the other escaped X5s for a long time, that her genetic code contains DNA preserved from his dead wife. She is not an exact duplicate, "more like inspired by".
Has Shibolena, the android created in the shape of Dr. Hinelar's daughter, Shizuka.
Earlier than that, Choudenshi Bioman had the Black Prince, who was created in the shape of Doctor Man's son, Shuichi. Subverted in that Shuichi is actually alive, and met the Biomen after the Black Prince's demise. In fact, his appearance revealed that Doctor Man was oncea man.
And in one episode of Taiyou Sentai Sun Vulcan, Black Magma builds a robot replica of a scientist's dead daughter in exchange for his creating a lethal poison. The robot eventually accepts the scientist as its father and refuses to kill him when ordered to, leading the villains to destroy it.
Dirk Gently: Subverted Trope, where Professor Jericho has built a voice-responsive Robot Kid named after his daughter, who died in a car crash. However the real Elaine is not really dead but in a coma, Jericho is in denial that she's not going to recover, and far from transferring his affection to the robot, he's planning to sell her to China.
K9 was created by Professor Marius to replace the dog he couldn't take to his new home, Titan.
Also used with K9 in a later episode; after bidding farewell to Leela and K9, the Doctor immediately takes out a box marked "K9 Mark II".
And again in the new series, with K9 Mark IV being given to Sarah Jane Smith immediately after the heroic sacrifice of K9 Mark III.
Also in the Doctor Who episode Journey's End, when Rose must return to the alternate universe she was trapped in for two years, The Doctor gives her a replacement copy created when he transferred his regeneration energy into his severed hand, and Donna touched it, creating a second Doctor
Not to mention, the whole ending of "Doomsday", where Jackie becomes alternate-Pete's replacement for alternate-Jackie, and alternate-Pete becomes Rose and Jackie's replacement for Pete, and Mickey becomes the replacement for Ricky (alternate-Mickey).
Also, in the Doctor's Daughter, Jenny could be seen as a replacement goldfish to his family on Galifrey, which he remarked had died previously. Though as far as the Doctor knows, he's lost Jenny as well, so not much of a replacement.
In the case of the First Doctor, he picks up Vicki, an orphaned young girl, immediately after losing his granddaughter Susan, and treats her like a surrogate. A couple of stories after Vicki leaves he picks up Dodo, who he takes an immediate liking to on account of her physical resemblance to Susan, despite her unusual stupidity.
The trope is frequently invoked any time the Doctor gets a new companion. The Doctor either expressly says he needs someone else with him or denies that the new companion is replacing the old. This trope is usually averted or subverted when the Doctor develops a genuine relationship with the new companion.
On two occasions the new companion has directly pushed back at being compared to a previous occupant of the TARDIS. Martha Jones became frustrated at the Tenth Doctor's continual invoking of Rose Tyler (who had been lost in a parallel universe). Clara Oswald says outright she doesn't want to be competing with a ghost when the Doctor indicates that she reminds him of a friend (actually a future "echo" of Clara named Clara Oswin Oswald) who had died.
In the episode "Man on the Street" (1x06), an Internet billionaire, Joel Mynor, uses Echo as a replacement for his dead wife Rebecca, but only once a year - the anniversary of her death in a car crash on her way to the new house Joel bought when he finally hit it big in business. Later, toward the end of "A Love Supreme" (2x08), Echo - who now can control the 40 personalities in her brain - briefly becomes "Rebecca" for the last time to give her blessing to Joel's remarriage.
In the episode "Instinct" (2x02), another Rich Dude rents Echo as a longer-term replacement for his wife and mother of his infant child; again, the client's wife had died too young (in this case, of complications from the birth).
Elvis And Slick Monty: Parodied. In one episode, Slick had to get a literal replacement goldfish after Dr. Leonate Elvis's old one while he is away, only for Leon to eat the replacement goldfish itself. With no time left to get another one, Slick stuck Dr. Leon's hand into the bowl. Elvis was fooled.
ER: When Luka flashbacks to when his wife and children were killed, viewers noted that his wife bore a resemblance to Carol Hathaway, explaining Luka' s attraction to her.
Eureka: In the second episode, it is revealed that a scientist (after his wife leaves him) makes a clone of his wife and acts as if she had never left, even having a child with the clone.
The Flash (2014): Caitlin's fiance Ronnie apparently died in the same accelerator explosion that put Barry in a coma. After Barry wakes up, he slowly gets more and more Ship Tease with Caitlin, and it's implied a few times that he reminds her of Ronnie (as they're both handsome, good-hearted scientists). In the Hate Plague episode, when Caitlin gets a little overprotective, Barry snaps "I'm not Ronnie!" While he apologizes later, she admits he has a point, and the Ship Tease dials back considerably.
Fringe: Peter Bishop. The Peter from our universe died as a child and in his grief, Walter, his Mad Scientist father, dragged an alt-reality Peter into our world as a replacement.
Ned himself is one. After his older brother, Brandon, was executed it fell to Ned to become Lord of Winterfell and marry Catelyn Tully.
Tywin tells Arya that she reminds him of Cersei when she was young, and something in his voice makes it sound like he regrets how things went. In the books, he and Cersei were originally quite close, but a series of events including Tywin failing to get her married to Rhaegar Targaryen and instead marrying her to Robert strained their relationship to the point it's at now.
The recently widowed Scott latches onto Katherine Bell, an old friend of his late wife, ignoring all signs that she's up to no good. Not until best friend Lucy produces undeniable evidence that she's a scam artist does he finally admit that he's been projecting his memories of his late wife onto her. Unusually for this trope, the two women looked nothing alike.
Similarly, Sonny fell for Hannah Scott because of her eerie resemblance to his late wife Lily (killed by a car bomb meant for him) and his late lover Brenda (killed in an entirely unrelated incident, but he blames himself anyway). While he admits to the strong similarities in their appearance, he's in denial about how much it affects him until the discovery that she's an undercover FBI agent and he realizes that she was no doubt assigned to him because of how much she looked like both women.
Happens to Katherine Bell again when Stefan Cassadine falls in love with her. Although he initially seemed genuinely interested in her, bit by bit, began to mold her into the image of his lost love Laura.
Hamish Macbeth: The episode "Wee Jock's Lament" has the title character's dog, Jock, run over and killed at the beginning of the episode. At the end of the episode, he ends up receiving another dog of the same breed as a reward for solving the crime of the week — and he names it Jock.
Hetty Feather: Polly is adopted from the Foundling Hospital by a rich couple because she resembles their recently deceased daughter.
King Of Queens: Unbeknownst to Doug, it's the reason his childhood dog is still around.
Knight Rider: A really unpleasant twist for Michael Knight occurs in the second season episode "Goliath". Turns out he's the replacement for his benefactor's rotten-apple of a son Garthe.
Law & Order: Criminal Intent: In the episode "Saving Face," a wealthy couple have a new kid to replace their treasured son, whom they view as having possessed Marty Stu levels of perfection. Their daughter is perpetually The Un-Favourite her entire life and eventually resorts to crime in her desperation to gain her parents' approval.
To make things worse, first off, she was born after the son's death, so she was The Unfavorite to a brother who had been dead her whole life and had never met herself. Second, and perhaps even more horrifying, is that the parents took this to the next level, expecting their daughter to live the life their son had mapped out for himself — a son who died at thirteen. She was literally held to a child's idea (and not even from herself as a child) of what he wanted to be when he grew up.
Law & Order: Special Victims Unit: In the episode "Locum", a couple is revealed to have adopted a orphan girl simply because she looked almost identical to their biological daughter who was lost years before. To make the newly adopted kid look as much like their lost child as possible, the parents (mostly the mother) forced the 8-12 year old to wear the girl's clothes, dye her hair, and even get a nose job. The kicker? The biological daughter is found by the police alive and, at the end of the episode, is returned to her parents as the replacement daughter watches on.
Lost: Juliet is made into this twice, both times by Ben. The first time, he tries to use her as a replacement goldfish for Jack's ex-wife Sarah to further his Mind Screw on him. Then before that, for himself as a replacement goldfish for his MIA childhood sweetheart Annie.
Malcolm in the Middle: Dewey did this in one episode with, indeed, a goldfish. Subverted Trope, since Dewey kept replacing the goldfish in order to fool his parents into believing he could reliably care for a pet so he could have a dog, and Inverted by his parents who kept replacing the live goldfish with a dead one.
Monk: Featured a literal replacement goldfish. Natalie's daughter, Julie, had a goldfish given to her by her father who was subsequently killed in combat. Natalie repeatedly replaces the goldfish so that the daughter won't lose this emotional link to her father. Unfortunately, she does this well beyond the average lifespan of the domestic goldfish, which Julie's science teacher notices.
NCIS: Tony has a goldfish named Kate, after a teammate who died early in the series.
Now joined by one named Ziva.
Newhart: "Hi. I'm Larry. This is my brother Darryl, and this is my other brother Darryl." You didn't even have to be adopted to be a Replacement Goldfish.
The Office (US): Following the one year Time Skip in the Grand Finale, we find out that Phyllis has been offering sweets to the new black employee who replaced the now-retired Stanley. During one of her confessionals, she then reveals that she's purposefully fattening the new kid up in hopes that he'll one day resemble Stanley, who she misses dearly.
One Foot in the Grave: Patrick adopts a dachshund after Pippa miscarries following a road accident. Pippa correctly points out that the dog is his "baby substitute".
One Life to Live: Within weeks after the stillbirth of her nearly term son, Cassie Carpenter found an abandoned baby in the manger scene of the town church (her husband was the local minister) and instantly declared that she was going to adopt him, even naming him "William", as she had intended to name her late son, clearly latching on to the new baby as a replacement for him. But when the birth mother came forward and changed her mind, the stress of the near-simultaneous loss of two babies triggered a nervous breakdown in which Cassie became convinced that the babies were one and the same.
The Outer Limits (1995): Subverted in the episode "Mary 25", wherein the sleazy boss of a robotics company murdered his wife prior to the episode and replaced her with a robot made in her exact likeness. However, his motive for this is clearly to cover up his murder of her, since he all but ignores the robot and uses a Robot Maid instead to satisfy his "needs".
Perfect Strangers: After breaking up, Balki and Mary Ann date people who are virtual carbon copies of their exes.
Revolution: In episode 10, it is revealed that Miles is this for Bass Monroe, replacing his entire family. Deconstructed Trope, because Monroe developed an unhealthy borderline erotic fixation on Miles, and when Miles betrays him (expanded on in the first season finale) as well as disowns Monroe for ever being family, Monroe just loses whatever pretense of sanity he had. Monroe failed to realize that Miles is not some pet, but a human being with his own feelings.
Scrubs: J.D. and Turk are very attached to their stuffed dog Rowdy, which Carla hates. As a favor to Turk to make up for hurting his feelings by insulting the dog, she offers to get him cleaned. On the way home, she loses the dog by not tying it to the top of her car securely enough. She then attempts to find a replacement.
And then the ruse falls apart when the real Rowdy is found... and J.D. and Turk are thrilled because now they can both have one.
Sisters: When she is contacted by the man who received her late-husband's heart, Teddy begins projecting her memories onto him. It ends when he declares that he deserves better than being used as a substitute and she sadly realizes that she either isn't over her husband's death or that it's too painful to be close to a part of him.
Sliders: A mad scientist in one episode was, in fact, his robotic replica without even knowing it.
Smallville: Adrian Cross and Gabriel Grant were both clones of Lex's deceased brother Julian. Lex shot the first and hired an assassin to kill the other. In the same episode.
Dr. Noonien Soong transferred his wife's mind into an android after she was fatally injured when they were fleeing the Crystalline Entity that destroyed the planet they live on, despite the fact that she was going to divorce him. He went to such extreme measures to make her seem human, even the most advanced technological equipment and everyone she ever met, except Data, couldn't tell the difference. Soong's wife was still the same person, but had unknowingly become a Tomato in the Mirror who would never find out. Data himself didn't know Soong's wife was an android until her arm came off.
Data himself is arguably a replacement for Lore.
Something similar happens in the episode Silicon Avatar with scientist, Dr. Kila Marr, who's son died on Omicron Theta -Data's home world- during the attack of the xcrystaline Entity. She goes from open hostility towards Data due to him looking exactly like Lore - who aided the Entity, towards seeing him as the last remnants of the child she lost, even going so far as to request he read her son's diaries... in his voice (Data, being the Emotional Emotionless Person he is, doesn't realise the psychological ramifications of this until it's way too late.)
One episode had Janeway mistaken for an alien man's dead daughter.
It ends up working out decently well for her; not only does he prevent her from being taken prisoner with Tuvok and B'Elanna, the man's devotion to Janeway and his desire to save his also dead wife from the prison where the Voyager crewmembers were being held ends up being what allows Janeway to rescue her people.
Trailer Park Boys: In season 8, Ricky decided to get a pet goldfish. Unfortunately, since Ricky is not the sharpest of knives, he thinks it's okay to share drugs and liquor with "Orangie". This sets off a panicked search by his friends to replace Orangie before Ricky realizes he's dead (they even bribe a veterinarian receptionist to claim that he's drunk and passed out). Later, we find that Bubbles has amassed a large stock of replacement goldfish, and replacing the latest Orangie has apparently become a common routine for him.
In Unbreakable Kimmy Schmidt, Kimmy has a sister who was born after she disappeared. Really the only thing that needs to be said is that her name is Kymmi.
The X-Files: The golem in the episode "Kaddish", specifically created by the fiancee of an assassinated man to "play" him in a fake wedding.