Bartuc the Bloody is the leader of a third wave of Council Members summoned by Baal inside the Throne of Destruction. Bartuc represents Act III in Baal's rundown before the final battle, and is accompanied by numerous council members. Possessing high lightning and fire resist is vital when fighting him and his ilk.
Warlord of Blood?Edit
It is possible that Bartuc was once the Warlord of Blood, a Vizjerei Mage who was in rivalry with his brother, Horazon. However, this is not certain. They both seem to be the same character because of the same name and same blood reference, but this Bartuc could just be a tribute to the Warlord of Blood. This Bartuc could just have acted similar to the Warlord and so earned a similar title.
The Legacy of Blood novel by Knaak (deemed canon by Blizzard Entertainment) makes it seem as if it is impossible for the Warlord to come back to Sanctuary without his armour. And since his armour was destroyed by Horazon just before Diablo entered Lut Gholein, Baal would not have had the armour to resurrect the Warlord of Blood.
Bartuc the Bloody is not wearing armour though, so it is possible that Baal just brought back half of his soul without the half in the armour. It is also possible that only the Prime Evils have the power to do that, while the Lesser Evils do not, because Belial was interested in reviving the Warlord but needed his armour to do so.