Maximillian Stael

Maximillian Stael was a scientist who, along with Adam Colby and Thea Ransome, worked for Dr Fendelman in studying "Eustace".

He had medical training, sufficient to conduct a post-mortem.

Maximillian was secretly the leader of a coven which worshipped the Fendahl. In July 1977, he led the ceremony which transformed Ransome into the Fendahl Core. When he saw his coven members being transformed into Fendahleen, he realised that it had all gone horribly wrong. His fate was sealed when he briefly locked eyes with the Fendahl and was overcome by a permanent, near-total paralysis. Realising he was doomed, he used a gun which the Fourth Doctor gave him at his request to commit suicide, saving himself from the fate of his brethren. (TV: Image of the Fendahl)

Behind the scenes
Although several sources spell his first name with one "l", it is spelled "Maximillian" in the credits.