Mawdryn Undead
"Mawdryn Undead" is the first of three loosely connected serials where the Black Guardian ( Valentine Dyall ) attempts to compel the alien Vislor Turlough ( Mark Strickson ) to kill the Doctor , and introduces Turlough as a regular character . 
<triplet> Vislor Turlough <subj> Mark Strickson <obj> performer