Timantha Turner is the gender-swapped alter ego of Timmy. In order to find out what Trixie wanted for her birthday, Timmy accidentally wishes himself into a girl so that he can find out what type of stuff girls like.
Timantha is the result of Timmy being unintentionally wished into a girl by Wanda, one of his fairy godparents. Timmy and Cosmo were making fun of girls which angered Wanda. Wanda quickly zaps him with her wand, turning him into Timantha. Timantha can think about "boy" things if she thinks really hard, but she mostly thinks girly thoughts.
Her hair is straighter than Timmy's but with two slight chips in it at the front (usually only one is visible), as well as a ponytail. She wears a pink headband with a bow, pink earrings, pink lipstick, long eyelashes, as well as a pink colored dress with a white blouse. Like Timmy her shoes are connected to her blouse/pants. Her voice is higher than Timmy's. Her fingernails are sharper than Timmy's, and she walks in an extremely exaggerated girlish manner, like a ballerina. When Timmy wishes himself into a girl, her mind is overcome with girlish thoughts (rainbows, clouds, unicorns, and other stuff) and she must concentrate to remember boy stuff (comic books, superheroes, etc.). He/she finds that Trixie Tang is secretly in love with comics, superheroes, etc.
Hoping to win over Trixie Tang's heart by getting her the gift she wanted most for her birthday, Cosmo suggests that Timmy could only think of the perfect gift for a girl is if he wished he was a girl. Timmy laughs saying it is a waste of a wish and insults girls which angers Wanda so much that she turns Timmy into a girl, resulting in Timantha (She later gets back at them by wishing Cosmo a woman and Wanda a man). She then went to the mall to shop for a gift for Trixie, when Timmy's boy thoughts got her side tracked and she ended up in a comic store, fighting over a comic issue with another girl. To her surprise, it was Trixie who was actually a tomboy who secretly liked boys' stuff, and above all else, she just wanted a boy that could talk to her and understand her. Timantha and Trixie become good friends, and when it seemed like she figured out what Trixie wanted, Timmy wished himself back to normal. Unfortunately for him, Trixie had her girl friends to talk to and didn't need a boy. Timantha also appeared in the console versions of Breakin' Da Rules to disguise himself as a Crème Puff (or the Girl Scout Organization Vicky is in charge of).
The name Timantha is a combination between Timmy and Samantha.
This is the first time when Timmy became a girl.
Another female version of Timmy is featured in the Elmerella comic strip in the June/July 2004 issue of Nickelodeon Magazine, where Timmy wishes to become Elmer's fairy..., and before Timmy completes his sentence, Cosmo turns Timmy into a fairy godmother. Timmy's female fairy form in this comic strip has a striking resemblance to Timmy's future daughter Tammy Turner, rather than Timantha.