Often, diminutive versions of names are used for children; however, their usage may diminish as the child ages, sometimes at the child's own request. If this occurs to a character in-series, it's usually either a sign of Character Development or the character trying to seem more mature than he really is.
The character's childhood nickname may end up becoming an Embarrassing Nickname as an adult. Compare to Meaningful Rename, which includes cases in which the character's name actually changes when they become an adult. If said name change is a culture-wide phenomenon, it's a Rite-of-Passage Name Change. Compare Significant Name Shift.
- In Bleach, Toshiro Hitsugaya dislikes it when his Childhood Friend Momo Hinamori calls him "Shiro-chan." He finally gets her to call him by his surname when he joins the 13 Court Guard Squads, but since he ends up shooting past her to the rank of Captain, he insists that she call him "Captain Hitsugaya."
- X-Men: In the "Days of Future Past" storyline, the future Kitty Pryde goes by "Kate" and sees the nickname "Kitty" as a relic of her childhood.
- Similarly in Marauders, she starts going by Kate after the shock of not being able to use Krakoan gates and the responsibility of smuggling mutants from oppressive countries into Krakoa by boat.
- A Silver Age Superboy story is about a college-age Clark Kent trying to avoid answering the question "Are you Superboy?" while hooked to a lie-detector. At the end of the story, he honestly answers that he's not Superboy, because he's decided he's now Superman.
- Subverted in the MAD parody of Teenage Mutant Ninja Turtles. When Danny asks not to be called by the name his father called him by for the entire film, his father asks if he'd prefer to be called by his proper name. It turns out that his father was so out of touch with his child that he didn't even realize he wasn't even calling Danny by the right name.
- Rock Stars takes place 10 years after Jem. Sheila no longer goes by her Misfits-era nickname "Jetta". All of the Misfits have moved past their "rebellious early 20s" stages.
- A Different Point of View: At age fourteen, Alan no longer goes by his old nickname "the Brain".
- Time Fixers: Nicktoons of the Future: In "Spongekira", after gaining a neural intelligence chip that makes him smarter, SpongeBob Jr. insists on dropping the latter part of his name as part of him undergoing Sanity Slippage. However, he continues to go by "Junior" once he's returned to normal.
- In Monsters University, the shy but sympathetic Randall Boggs goes by Randy. In the original movie Monsters, Inc., he is no longer called that way. This somewhat shows a character development, in comparison Mike and Sully have kept their nicknames, Randall has clearly lost his innocence and sympathy for Mike.
- In the film Under The Same Moon (La misma luna), the protagonist's mother comments that he is growing up so quickly that she will soon have to start calling him "Carlos" instead of "Carlitos". He stays Carlitos for the duration of the movie, though.
- Fantastic Four: Rise Of The Silver Surfer: The Human Torch is known as Johnny Storm for all of the first film. In the second, he has embraced the money that comes with sponsorship, and because "focus groups say Johnny skews young", decides to go by John Storm instead since he doesn't want "hero to children" to outweigh "ladies' man".
- The Hand of God: The Coming-of-Age Story theme is emphasized near the end when Antonio Capuano, the director, tells teenaged Fabietto that he should start going by his real, grownup name "Fabio".
- In Lady Bird, the titular character abandons her self-proclaimed nickname and starts going by her given name, Christine, when she goes to college, a time when she starts to realize the negative effects of her previous stubbornness.
- By the end of the first Teenage Mutant Ninja Turtles movie, Daniel "Danny" Pennington, after Character Development, tells his dad, "It's just Dan now."
- In the To Kill a Mockingbird sequel, Go Set a Watchman, Scout no longer goes by her tomboyish childhood nickname. She goes by "Jean Louise".
- Subverted with Ravenpaw in Warrior Cats. He fled ThunderClan not soon after becoming an apprentice, when he was still the cat equivalent of a teenager. He never became a warrior and thus never received his 'adult name' (all apprentices are called "[x]paw"). Ravenpaw however continued to use that name even after becoming a loner.
- Billy the Werewolf is a recurring character in The Dresden Files from the second book onward. He enters the story as a teenager who gains shapeshifting powers with his friends, the Alphas. As time goes on, Billy begins going by "Will", which the Alphas also call him. It's a significant turning point in his and Harry's relationship when Harry finally shifts from "Billy" to "Will" himself.
- The belief in this is used as a sign of immaturity in Otherwise Known as Sheila the Great, where the image-obsessed Sheila hates the fact that her father goes by "Buzz" and tries to convince him to go back to "Bertram", even though even she admits to preferring "Buzz".
- In the Little Women series of books, nicknames were needed for the twins John Brooke, Jr. and Margaret Brooke (sharing their parents' names requires the nicknames). Eventually Demi (short for Demijohn, he's half a John) and Daisy (a common nickname for Margaret) were chosen to fulfill Theme Twin Naming requirements. Upon reaching adulthood Demi went back to John (his father being dead by this point prevents confusion), but Daisy remains Daisy.
- In Star Trek: The Eugenics Wars by Greg Cox, Khan Noonien Singh is mainly referred to as "Noon" when he's younger, and working for Gary Seven. After the Union Carbide disaster in Bhopal, he resigns from working for Gary, telling him, "Stop calling me Noon. That was a child's name. My name is Khan."
- In his semi-autobiographical book The Life And Times Of The Thunderbolt Kid, Bill Bryson talks about himself and his parents in the third person:
They named him William, after his father. They would call him Billy until he was old enough to ask them not to.
- Survivors: When a stray dog's back teeth grow in, they rename themselves in a Naming Ceremony. The same applies to Leashed Dogs when they're given new names by longpaws. It's usually considered an insult to call a dog by their pup name, such as when Lucky angrily refers to his sister Bella as "Squeak".
- Isaac Asimov's "Profession": George and Trevelyan both had nicknames when they were eight, and they're shown to grow up by discarding their nicknames by the time they're eighteen.
- Inverted in The Curious Incident of the Dog in the Night-time - Christopher used to refer to his parents as Mummy and Daddy, but as a teenager he called them Mother and Father.
- At the end of Wolf of the Plains, upon becoming Great Khan, Temujin decides he needs a better name. Genghis is good.
- The same thing happens in the Emperor books, by the same author. Partway through The Gates of Rome, Gaius is accepted as an adult by the other Romans, indicated by them referring to him as Julius, like his father. At the end of the book, Marcus completes his initial tour of duty, marking him as an adult, too; as such, he starts going by Brutus.
- Jimmy Olsen in Supergirl is presented several years older than he usually is and is far more mature than most depictions. He goes by "James" instead of "Jimmy".
- The Suite Life of Zack & Cody: In "Super Twins", a wish on a star turns Zack and Cody into superheroes, and Mr. Moseby into a supervillain; at one point, Moseby turns Bob into a suit-wearing adult who prefers to be called Robert.
- Implied in an episode of Law & Order: SVU, when Stabler asks about his son by a nickname, and his wife tells him that he hasn't been called that for years (making it clear how little time he spends with him).
- Inverted in Doctor Who. Amy Pond was named Amelia as a child, but grew to dislike it for being sounding too much like it was out of a fairy tale.
- In the final season of Rizzoli & Isles, Frankie is having something of a crisis of identity. During a heart-to-heart with Korsak, Korsak suggests that maybe he should stop going by Frankie, which is what his family has called him since childhood. By the end of the series, he has started going by Frank.
- One episode of Girls in Love has Ellie persuade her father to cease calling her "Elly Belly".
- On Supernatural, Sam objects to being called Sammy, correcting anyone who calls him by that nickname. Eventually, he concedes the nickname to his older brother, but it becomes a Berserk Button for anyone else using it. However, he also dislikes anyone calling him Samuel, the long form of his name.
Sam: You know, Sammy is a chubby 12-year-old, OK? It's Sam.
- The Big Bang Theory: Sheldon's older brother George Cooper, Jr. no longer goes by "Georgie". Sheldon, of course, won't have it.
Sheldon: Hello, Georgie.
George: It's just George now.
Sheldon: Fine, George. No, I don't like it. Georgie.
- The Wonder Years: Winnie Cooper makes the decision to go by her given name "Gwendolyn" after her brother is killed in Vietnam.
- On All My Children, Adam Chandler III went by "Little Adam" until he was a preteen when he announced that he wants to go by A.J. instead of "Little Adam", simply because it sounded too babyish.
- The Twilight Zone (1959): At the end of the episode "Nervous Man in a Four Dollar Room," cowardly gangster Jackie Rhoades is replaced by his reflection from the mirror, a brave, dignified, morally upright version of himself. Henceforth, he calls himself "John," not "Jackie."
- In episode 3453 of Sesame Street, Baby Bear decides to change his name to "Not-a-Baby Bear", because he isn't a baby anymore and doesn't want his friends to get the wrong impression. He soon finds out the disadvantages of changing his name, such as not getting a package of instant porridge from his Grandma, and how different his fairy tale, "Goldilocks and the Three Bears", sounds. He soon learns from his friends that your name doesn't always have to mean what you are, and that Papa Bear went through a similar experience in his childhood, as his name was also "Baby Bear" once. These persuade Baby Bear to be proud of his original name.
- In Animal Crossing New Leaf, if you upgrade their shop to T&T Emporium, Timmy and Tommy will start going by their full names (Timothy and Thomas) on the town billboard.
- In Valkyria Chronicles, Welkin dislikes being addressed as "Welkies".
- Tales of Berseria: The childish character Laphicet, going by "Phi" until that point, requests that the nickname be abandoned because he finds it too childish. (It's difficult to categorize this one because Laphicet is 1) an angel who was incarnated only twelve years ago, and 2) the Replacement Goldfish for the main character's younger brother, and sharing his name. And his resistance to the nickname "Phi".)
- In the video game adaptation of Danny Phantom: The Ultimate Enemy, Danny's evil future self Dark Danny receives an Adaptation Name Change to "Dan Phantom".
- Implied in Persona 4. Eri Minami spends most of the Temperance Social Link calling her young stepson Yuuta "Yuu-kun." As Yuuta and Eri finally get past their differences and start bonding, she switches to calling him "Yuuta" instead. Since their relationship improves from that point on, it seems as though Yuuta preferred that Eri call him by name rather than try to endear herself to him by using a nickname.
- Kenta from No Need for Bushido at one point gets mocked for having "a baby name" but this turns out to have a tragic origin, since his entire clan was wiped out when he was a child so he was never able to receive a "proper" adult name. It symbolizes how he's never moved on from the tragedy and how it's stunted his emotional maturity.
- Cyanide & Happiness references this with "The life cycle of Roberts", outgrowing nicknames Bobby, Robby and Bob in succession.
- Like all succubi in Sinfest, Baby Blue was named after her color. However, major Character Development led to her becoming The Devil's right-hand lady, and "Baby" was ditched.
- In Alice Isn't Dead, the episode "The Factory" has the narrator enter the titular factory and meet a young man named Jackie, except every time she loses sight of him and finds him again he grows several years older, and when she addresses him as "Jackie" after he becomes middle aged, he requests to be called "Jack" instead.
- In the Foster's Home for Imaginary Friends episode "The Bride To Beat", Bloo fears that Mac is outgrowing him and decides to act like an adult. This includes changing his name from "Bloo" (short for "Blooregard") to "Bob".
- SpongeBob SquarePants:
- In an episode where SpongeBob begins wearing longer pants, and thus seems more like a mature adult rather than a Manchild, his sophisticated peers begin referring to him as "SpongeRobert".
- In "Mermaid Man and Barnacle Boy V", Barnacle Boy does a FaceHeel Turn because Mermaid Man keeps treating him like a kid, despite both of them being elderly, and demands to be known as Barnacle Man. Mermaid Man eventually agrees, but this is forgotten in later episodes.
- There's a woodchuck character on Animaniacs who wants to be taken seriously as an actor and insists on being called Charleston instead of the Embarrassing Nickname Baynarts.
- The Flintstones: Whenever Fred tries to act sophisticated, he tends to calls himself and Barney "Frederick" and "Bernard".
- After starting college in Ben 10: Omniverse, Gwen starts going by "Gwendolyn".
- Discussed at the end of the Teen Titans episode "The Beast Within". Beast Boy mentions that, after what he experienced in the episode, maybe he should change his superhero name to "Beast Man".
- Mickey Mouse (2013): In "The Fancy Gentleman", Mickey is taught to act more refined and starts calling himself and Minnie "Michel"note and "Minifred"note (one of the very few times their full names have been referenced in-series).
- Enzo Matrix in ReBoot calls himself just Matrix after growing up in the games, as well as becoming cynical and hating the naive child he used to be.
- The Legend of Korra:
- In the Family Guy movie "Stewie Griffin: The Untold Story", Stewie encounters his adult future self, who now goes by the name "Stu".
- Real life child stars Billy Mumy, Ricky Nelson, and Ricky Schroder dropped the "y" from their names when they became grown up stars. Larry Fishburne, who started acting in his teens, eventually started going by Laurence Fishburne.
- Barack Obama used to go by "Barry" in his youth. He eventually asked to be called by his real name; this was as much about reconciliation with his racial/ethnic identity as his age/maturity.
- John Williams' early work as a jazz pianist was credited as "Little Johnny Love" Williams. When he started writing music for TV, it was shortened to "Johnny Williams," and he dropped the diminutive altogether once his film career started taking off.
- Alexandria Ocasio-Cortez during her teenage years went by "Sandy", a diminutive of Alexandria. She now goes by Alex if you actually know her personally.
- For a while, Joey Lawrence ditched his name Joey and decided to go by "Joseph"; he eventually went back to being addressed as Joey.
- Rapper Lil' Bow Wow started going by Bow Wow at the age of 16.