Kelbor was the head of the Admech during the Heresy. He apparently survived and then did nothing for 10k years. (This is actually quite common)
Arik was the head of the thunder warriors and survived the culling (after the conquest of Earth the big E turned on the thunder warriors and had them effectivly wiped out, presumably by the Custodes) and then gained immortality during the heresy then dropped off the grid.
Eldrad is the most powerful Eldar pysker. Widely considered a jerk.
Drago is a super special grey knight paladin.
Vect is the head of the Dark Eldar.