April O'Neil

Background

April is a friend and ally of the Teenage Mutant Ninja Turtles.

Due to there being many continuities involving the turtles April has always been modified slightly to fit the medium.

Originally sporting dark brown/black hair she was a computer programmer that worked for Baxter Stockman. After being saved by the turtles they became friends and she continued to aid them in whatever means possible. Including giving them a place to hide and sacrificing her home when the Shredder attacked looking for the turtles.

She and Casey Jones are romantically involved. They have adopted a child named Shadow. April was injected by nanobots by Baxter in vol. 2 of the comics. In vol. 4 it was revealed that the nanobots had sterilized her and were slowly killing her. The nanobots were eliminated by turtle-controlled nanobots but sterility remained. 

In "Teenage Mutant Ninja Turtles Adventures" by Archie Comics, April received training in the martial arts by Splinter and became a competent warrior in her own right.  at one point April was even mutated into a Turtle by aliens, becoming the 5th turtle, she wore a white bandanna armpads and kneepads while she was a turtle , but her humanity was ultimately restored.