Some TMNT stuff was always meant for grownups.
In the original Mirage Comics storyline for Eastman and Laird's Teenage Mutant Ninja Turtles, April O'Neil (who originally sported a jumpsuit) was a skilled computer programmer and started out as an assistant for the villainous scientist Baxter Stockman. April O'Neil already proved in her teens a flair for computers and was a clever hacker. At the age of 27 years, her work began life as a laboratory assistant to Baxter Stockman, to which she helped program his Mouser robots, but when she discovered that Baxter was using his Mousers to burrow into bank vaults and steal from them, she attempted to flee Baxter's workshop and found herself in the sewers running for her life, with several Mousers in pursuit. Three of the Turtles happened to come across her and save her and brought her back to their lair, where she would meet Splinter and found out about their origin. With her new friends, she returned to Baxter's hideout and defeated him. The Turtles later successfully fended off a Mouser invasion after Baxter programmed the Mousers to attack them. As the series went on, though their various adventures together, she became a closer friend to the Turtles and their link to the outside world. The Turtles also lived for a time with April when Splinter disappeared.
After leaving her job with Baxter, she decided to reopen her father's antique store she inherited 'Second Time Around'. During the Shredder's sudden return (What Goes Around... Comes Around!/Silent Partner/Return to New York story arcs) the shop came under attack by The Shredder and the Foot Clan (who had come for the Turtles), and was destroyed in the ensuing battle. April, the Turtles and their new friend Casey Jones had to escape to Casey's family farm house in Northampton, Massachusetts where she later had nightmares about the Foot Clan's attack.
A relationship that greatly influenced April was that with Casey Jones. Initially, the two could not stand each other, but during these events she would know Casey better and in time take a liking to him. During the mid-90s, April would live with her sister Robyn for a while during the events of City at War and find out their father died. Looking for a new place to live, she just happened to find the apartment Casey was living in. Eventually she'd marry Casey and they'd raise his adopted daughter Shadow Jones together as a family.
In TMNT Volume 2 of the series, April would be attacked and injected by Baxter Stockman, now a brain inside a huge killer robot (apparently, Baxter having escaped capture, had placed his brain in the body of a robot and sought the turtles out in order to get revenge on April's escape from capture). She would be injected with something, and though the Turtles defeated Baxter, it was never revealed what exactly April was injected with.
This would be somewhat revealed in TMNT Volume 4, as April and Casey wondered why they couldn't have children and discovered deadly nanobots within her system, threatening her life. With help of the Utroms, the Turtles made TMNT-style Nanobots that saved April's life before Baxter's nanobots could reach her brainstem. Time would pass and April still couldn't have children. After a few studies were conducted, they found that April is not the biological daughter of her parents.
This put an emotional strain on April, and she became a female version of Nobody until she was discovered and unmasked by her husband Casey.
It was with the help of Renet taking her back in time that revealed that April was really a living drawing, brought to life with the help of Kirby's crystal, drawn by her father, who at the time really wanted a daughter. This was before their own biological daughter Robyn O'Neil would be born. Unlike Kirby's drawings drawn with pencil that would vanish after a while, April's father used a pen, so it might explain why April lived past thirty without vanishing so far. This realization had hit hard, questions such as if she was real or not, whether she could live or die, or when she would eventually vanish were too much for her to handle so she then went on a self-discovery trip. April bid farewell to Shadow and Casey and went to be alone with her thoughts in Alaska. Although the trip helped April cope with her demons, and led to her eventual return to New York City, her family history remained unexplored. She declared to Casey and Shadow what she had learned, before she set off again on her journey
The narrative structure created by Mirage Studios ended when the company sold the copyrights to TMNT to Nickelodeon.
Fan reaction was mixed, as many believed her normality served as a good contrast to the fantastic nature of the Turtles. No other incarnation of April has shared this origin to date.
Unlike some of the other versions of her character, the Mirage Comics version of April has dark brown/black hair (though early color reprints of Volume 1 depicted her hair color as red/light brown). Most future incarnations of April that came afterwards are redheads.
- Originally April was going to be Asian, but later was changed to her Irish-American design.
- April's first name was given to her in memory of Kevin Eastman's African-American girlfriend at the time. In particular, her appearance in issue #4 looked ambiguously African-American or Latina.