Ptolem

Professor Ptolem was the Thal scientist in charge of the Dalek research into the Mutant Phase, as they thought any contact with it would affect them. With help from the Fifth Doctor and Nyssa, he discovered the cause of the Mutant Phase, then travelled back through time to complete the research. (AUDIO: The Mutant Phase)

Behind the scenes
Ptolem originally appeared in the Audio Visuals story of the same name, voiced by Tim Beckerleg.