Short answers, pulled from the story.
April O'Neil is a fictional character and the first human ally of the Teenage Mutant Ninja Turtles. She made her debut in the Mirage Comics series in 1984 as a computer programmer who fled her employer Baxter Stockman after discovering he was using her robots to rob banks, and was subsequently rescued by three of the Turtles in the sewer.
April O'Neil was voiced by Renae Jacobs in the 1987 animated series. Jacobs auditioned for the role in Los Angeles in 1986 and was initially rejected by voice director Stu Rosen, but the producers chose her recording after hearing it last among the candidates.
April O'Neil has been played by four actresses in live-action films: Judith Hoag in the 1990 film, Paige Turco in the 1991 and 1993 sequels, and Megan Fox in the 2014 film and its 2016 sequel. Malina Weissman also appeared as a younger version of the character in the 2014 film.
In the original Mirage Comics, April O'Neil was a computer programmer and assistant to the scientist Baxter Stockman. She helped program his MOUSER robots before discovering he was using them to burrow into bank vaults, after which she fled and was rescued by the Turtles.
In the 2012 animated series, April O'Neil possesses psychic abilities tied to her half-human, half-Kraang-mutant biology. Her mother was abducted and experimented on by the Kraang before April was born, leaving April immune to mutagen and capable of detecting sensory information beyond even Splinter's superhuman hearing. Her psionic abilities were first hinted at in Episode 7, "Monkey Brains."
Ayo Edebiri voiced April O'Neil in the 2023 CGI film Teenage Mutant Ninja Turtles: Mutant Mayhem. She reprised the role in Tales of the Teenage Mutant Ninja Turtles, the 2024 animated series sequel to that film.