In Diablo III, what is the name of the first boss fought in the game’s campaign?

In Diablo III, the first major campaign boss is the Skeleton King.

The Skeleton King is encountered in Act I, inside the Cathedral. His identity is tied to King Leoric, a ruler who became undead after the corruption surrounding Tristram. The encounter is part of the early campaign and introduces players to the game’s recurring themes of fallen rulers, demonic influence, and reanimated armies.

The Skeleton King is not the same character as the Butcher, another famous Diablo enemy who also appears in Act I. In Diablo III, players must complete the Cathedral storyline and defeat the Skeleton King before the campaign moves toward later threats, including the assault on Tristram and the confrontation with the Butcher.