Lyle Bolton - Batman: The Animated Series

Formerly a "respected" head of security at Wayne Enterprises, Lyle Bolton was appointed chief of security at Arkham Asylum at the recommendation of Bruce Wayne. 

However, his cruel and abusive treatment of patients led to disciplinary action and dismissal. 

Furious, Bolton vowed revenge—not on the patients, but on those he blamed for Gotham's villainous community: the police, politicians, press, and doctors who failed to permanently eliminate the city's costumed criminals.

After disappearing from public life for six months, Bolton resurfaced as the vigilante "Lock-Up," claiming to be Batman's greatest ally and Gotham’s ultimate jailer. Taking several people hostage, including Mayor Hamilton Hill, Summer Gleeson, and Commissioner Jim Gordon, he intended to execute them.

Defeated by Batman and Robin, Bolton was sent to Arkham Asylum. He happily accepted this, convinced that this was where he belonged—keeping a watchful eye on Arkham’s patients from inside its walls.