Nefarkus was... is a powerful bloodmancer, one of the strongest. A great loss in the war against the Ghuls and Geists. He was the first one to cut off the corrupted anima system from the rest. Unfortunately, he got corrupted himself. He knew the risk, and he even tried to kill himself before the corruption took over, but unfortunately for us, his blood was too strong to burn. He rose from the ashes and slaughtered every single one of his followers.
Now he is leading the massive hordes of Ghuls, he seems to still be conscious of his actions, almost as if he chose to join the Ghuls. He is able to control vast groups of these monsters and uses his infamous blood magic to resurrect and heal them. He even managed to break into one of our Blood Chambers and steal a Blood Altar. He just broke the whole thing off the ground and took off on it. He now flies around on this altar and spreads his blood to all the Ghuls, it seems to empower them. I just hope we are able to stop him soon.