I mean, technically he is just a lich... Who so happens to have a cult that worships him, which somehow gave his incorporeal spirit power during his short absence after the defeat at the hands of his right-hand lieutenant, Kas, and has absorbed the power of a lesser deity to use as his own while escaping from imprisonment by the Lady of Pain for a failed plot to usurp the cosmic order when he infiltrated Sigil, the City of Doors.

So, not a god, just a lich with the power of a God.

Haha petty semantics!