Wrackblight

Wrackblight, Seneschal of the Plague, is a disgusting and bloated daemon prince of Nurgle. Long ago Wrackblight was a mortal who pleased Nurgle with his research into biological warfare. His work devastated entire continents, turning city after city into a necropolis overnight, each the resting place of millions of the bloated dead. The stench of decay was so terrible that it reached all the way to Nurgle’s manse, where the Grandfather of Disease became aware of Wrackblight's murderous work. So pleased was Nurgle with what he saw that he immediately granted Wrackblight the gift of daemonhood.

Now Wrackblight serves Nurgle by harvesting the souls of those who die as victims of biological warfare. These poor unfortunates are compelled to serve the daemon prince for a year and a day as a Mancubus, a diseased and twisted creature that flits about on fly-like wings, covering Nurgle's enemies in a corrosive gas they extrude from their withered stumps of arms.