From Guild Wars Wiki
The Rogue Bull is an animal that requires defeating as part of the quest A Mesmer's Burden. His pet name is Bill. He belonged to Old Mac. He will respawn until you kill him with the quest active, after which he will not return.
- Ascalon (pre-Searing)
Quests involved in:
 During Annihilator 2: Searing Day
- The Rogue Bull has 80 health.