Which Zul'Gurub raid boss originally cast the Corrupted Blood debuff?

The Zul'Gurub raid boss that originally cast the Corrupted Blood debuff was Hakkar the Soulflayer.

Hakkar is the final boss of Zul'Gurub, a World of Warcraft raid introduced on September 13, 2005. During the encounter, Hakkar cast Corrupted Blood on players. The effect damaged its victim and could spread to nearby characters, but it was intended to expire or remain contained within the raid zone after the battle.

A programming oversight allowed infected hunter and warlock pets to retain the debuff when dismissed. When players later resummoned those pets in busy cities, Corrupted Blood escaped Zul'Gurub and spread through Azeroth. Non-player characters could carry the effect without dying, helping transmit it to players. Blizzard eventually contained the outbreak through emergency fixes and server resets.

The incident is often confused with a normal disease mechanic or with another classic raid boss. Hakkar's encounter deliberately used blood-draining abilities as part of its design, making the debuff central to the fight rather than an unrelated status effect.