After unceremoniously dumping Sarah Jane on earth, the Doctor believed he would be traveling alone for awhile, but then along came Leela in The Face of Evil. At first glance, Leela is a savage warrior from the Sevateem tribe on an unnamed planet, but we soon learn that her tribe are the descendants of an earth starship that had crashed landed on the planet. Over many generations, scientific knowledge was lost in favor of the fighting skills necessary for survival in a harsh environment. Leela barged her way into the TARDIS at the end of the episode and joined the Doctor on his adventures.

Though she was for all intents a primitive, Leela was highly intelligent and able to translate complex concepts into terms she could relate to. Despite the Doctor's attempts at "civilizing" her, however, Leela was strong-willed enough to continue in her savage ways. She usually dressed in animal skins, and was armed with a knife or a set of poisonous Janis thorns which she did not hesitate to use on people who threatened her, much to the Doctor's disapproval.

Leela's cunning and uncanny ability to sense danger proved useful on many adventures with the Doctor. However, when the Doctor returns to Gallifrey to face a Sontaran invasion, Leela decides to stay behind with Andred, a native Gallifreyan she has fallen for.