Leela was a warrior of the savage Sevateem, a tribe of regressed humans. She joined the Fourth Doctor on his travels, and with him fought for good causes. She knew little of technology and was continually amazed by her surroundings and the tasks she faced. Leele never lost her primitive edge and remained quick to take up arms throughout her time with the Doctor.
She left the Doctor after she fell in love with Andred, a member of the Chancellery Guard on Gallifrey, choosing to remain there to live with him. K9 chose to stay with her as well.
Leela was primitive, yet also very smart. Despite the Doctor's efforts to "civilise" and educate her, she kept her savage ways. She translated advanced ideas into terms she could understand. She usually dressed in animal skins and was armed with her knife and Janis thorns, which she did not hesitate to use, despite the Doctor's disapproval. Leela ranks as one of the most violent companions, regularly threatening or using deadly force against other humanoids. Although other companions have killed, Leela remains the only TV companion to be shown killing on a frequent basis.
Leela was first conceived by producer Philip Hinchcliffe and script editor Robert Holmes. They wanted someone in the mould of Eliza Doolittle in George Bernard Shaw's play Pygmalion: a bright but unsophisticated primitive who would learn from the Doctor. Writer Chris Boucher had submitted a story proposal entitled "The Mentor Conspiracy" which featured a character named Leela which fit Hinchcliffe and Holmes's ideas.
Although The Mentor Conspiracy was not produced, Boucher reused the character of Leela for The Day God Went Mad (later renamed The Face of Evil), seeing her as a mixture of Emma Peel from The Avengers and Leila Khaled. Boucher was asked to write two endings to the story, one where Leela left with the Doctor and one where she stayed behind. The decision to have Leela become a companion was made soon after.
Initially, Leela was to have only appeared in three stories. It was later decided that she would stay for all of Season 15. One consequence of this decision was a plot contrivance being added to Horror of Fang Rock to allow the character's eye colour to change, so that actress Louise Jameson would no longer have to wear uncomfortable coloured contact lenses.