Were you looking for the eponymous quest? See Archbishop Lazarus.
The Archbishop Lazarus was an ambassador from the Zakarum Church and an advisor to King Leoric who was corrupted by the Prime Evils. According to the manual to Diablo II - in the form of a letter from Sankekur - Lazarus was the Custodian of Mephisto's Soulstone in Kurast some time prior to his arrival in Khanduras. It was Lazarus who insisted, and eventually persuaded, Leoric to make Tristram the new capital and set up court in the abandoned Monastery. Lazarus was lured into its depths by Diablo, where he proceeded to shatter the soulstone that imprisoned the Prime Evil. After Diablo failed to fully possess Leoric himself, Lazarus brought the King's son, Prince Albrecht, into the labyrinth to serve as the mortal host for the Lord of Terror. After Leoric's death, Lazarus emerged from the Monastery's depths and rallied the villagers into a mob to find Albrecht - but the treacherous Archbishop led them right into the lair of the Butcher.
After this disastrous incursion, Lazarus vanished deep into the Monastery, where he remained, guarded by demonic minions. He was ultimately brought to justice by Aidan, Blood Raven, and their Vizjerei ally, who had managed to piece together the truth about what had happened.
Archbishop Lazarus in Diablo 1 cinematic
Stats
Archbishop Lazarus: Unique Advocate Mage
Resistances: Lightning, Fire
Immunities: Magic
Life: 600
Dungeon Level: 15
Damage: 30-50