A. St. John D. Caldera

Professor A. St. John D. Caldera was a neurologist whose mind was stolen by Skagra at the Think Tank space station. He died in the destruction of the station.

However, Caldera's mind lived on in the Sphere. After the Doctor defeated Skagra, he took the Sphere to Dronid, where he had the minds of Caldera and the other victims of the Sphere transplanted into new bodies. (WC: Shada; AUDIO: Shada; HOMEVID: Shada)

Behind the scenes

 * In the novelisation, Caldera becomes a woman, Daphne Caldera. Her speciality is 6-dimensional wave equations, instead of neurology.
 * A is a sunken area left behind by a volcanic eruption. The names of Caldera and the other Think Tank scientists are all derived from locations or geographical features associated with the volcanic Greek island Santorini.