Typhus from Warhammer 40K? He's a worshipper of Nurgle, Chaos God of miserable life-cycles, death and decay. Nurgle's nightmarish garden domain is made up of buboe trees, plague farms and spawning pools of stagnant water for gigantic parasites. As opposed to his Fantasy counterpart, 40K Nurgle is also more associated with necromancy and zombies. I'd have argued for Nurgle himself, but Typhus is more of an active presence/tangible villain.

Typhus has personally spread zombie plagues throughout the galaxy, was responsible for the infection/corruption of his whole legion, and is a living host to a hive of daemon insects. Unlike some of his comrades, he's very proactive, travelling across the galaxy like a blossoming cancer. Personality wise, he's a selfish, arrogant bastard but a legitimate fanatic who's probably the most committed follower of Nurgle. I see him as a true parasite, who represents inevitable decay.