Imogen Quaye

 was a teen-aged girl of moderate to low intellectual capacity who was part of an experiment to improve the capacity of the human brain.

Imogen's parents had died when she was twelve. She lived with her aunt who, when Imogen was sixteen, sold her to the Lashley Institute for 15 million euros.

As a result of the experiment, Imogen's brain capacity dramatically increased over the course of a month. Her memory improved, her ability to process information increased, she had no need of sleep, and, unknown to the researchers, she developed telepathic abilities.

Imogen used her telepathic abilities to convince her aunt and the three researchers to commit suicide. Recognising herself as a murderer, she was ready to kill herself, but the TARDIS dematerialised in her room. The Fifth Doctor explained that the TARDIS had recognised an intelligence comparable to its own and brought the Doctor here. He tried various arguments to talk Imogen out of suicide, but when he had almost convinced her, Donald Kelt, head of the project, arrived. He promised that Imogen would not be punished, but wanted her to undergo more surgery. When she refused, he threatened her with incurable mental diseases. In anger, she killed him.

The Doctor convinced Imogen that her aggression was gone. As he prepared to leave, he reminded her that humanity had still not cured several mental diseases. She decided to spend her life in search for cures. (PROSE: Artificial Intelligence)