Diane Whittlesey is Oz's first female officer and divorced single mother, who has suffered spousal abuse, poverty and substance abuse; through all of that she gained a pretty good understanding of criminal life. She is a CO in the Oswald Maximum Security Penitentiary, but she only works there because she can't find work anywhere else.
Her only drive is taking care of her mother, who has cancer, and her young daughter, whom she has to raise all by herself. She works double shifts, sometimes sleeping in the prison, just to make ends meet. Whittlesey is the only primary character who, although she was on for three seasons, was never killed off. She is one of the few characters to have a happy ending to their storyline.