A. S. T. Thira

A. S. T. Thira was a psychologist whose mind was stolen by Skagra on the Think Tank space station. He died when the station was destroyed. (TV: Shada)

However, Thira's mind lived on in the Sphere. After the Doctor defeated Skagra, he took the Sphere to Drornid, where he had the minds of Thira and the other victims of the Sphere transplanted into new bodies. (PROSE: Shada)

Behind the scenes
The names of Thira and the other Think Tank scientists are all derived from locations or geographical features associated with the Greek island Santorini. Thira is a classical name for Santorini.