In Diablo IV, Lord Zir is the vampire lord leading the Season of Blood storyline.
Season of Blood was Diablo IV’s second season and introduced a vampire-themed threat to Sanctuary. The seasonal story follows investigations into vampire attacks and the rise of dangerous blood-powered enemies. Lord Zir stands at the centre of that storyline as its principal vampire antagonist.
The season also introduced Vampiric Powers, which players activated and improved using seasonal systems and Pact mechanics. Lord Zir is distinct from other vampiric enemies such as the Blood Seekers and the Blood Bishop. Seasonal stories and mechanics are separate from Diablo IV’s permanent campaign, so completing the original campaign is not the same as completing Season of Blood’s narrative.