Angus MacKay
From Tardis Wiki, the free Doctor Who reference
Angus MacKay (15 July 1926-8 June 2013[1]) appeared in two Doctor Who television stories, portraying Borusa in The Deadly Assassin and Brendon Public School's headmaster Mr. Sellick in Mawdryn Undead, the latter of which saw him briefly portray the Black Guardian when he took on Sellick's appearance in a dream sequence.