Perpugilliam "Peri" Brown (Nicola Bryant)
Perpugilliam Brown, known as Peri, was an eighteen year-old American Botany student holidaying in Lanzarote with her step-father, when the Doctor and Turlough landed nearby. Turlough rescued Peri when she tried to swim to shore from her uncle's boat, and took her inside the TARDIS to recover.
The TARDIS took off with Peri still on board. Headstrong and argumentative, Peri stayed with the Doctor and helped him through his most difficult regeneration to date. Peri's demise is unclear.
During the Doctor's trial we saw Peri killed while an alien being was in possession of her body. This evidence is of dubious veracity, though. The Inquisitor reassured the Doctor that, in reality, Peri married the Krontep warlord Yrcanos.