Skarn

Skarn, the Herald of Terror, is the primary antagonist of Diablo Immortal.

"The demon known as Skarn, Herald of Terror—once Diablo’s most powerful lieutenant—is rallying a new demonic army. Skarn intends to gather the fragments of the corrupted Worldstone and use them to resurrect Diablo, reigniting the Eternal Conflict between angels and demons.

Skarn is not the only one hoping to seize the window that’s been opened by the Worldstone’s destruction; a fledgling Coven is at large, and dark cultists roam the land, spreading corruption wherever they go."

- from the official site