Oberon is the ruler of the Third Race, A race of magical shapeshifters native to the mystical island of Avalon. He became their ruler after deposing his mother, the insane Queen Mab, Avalon's original ruler.
After defeating Mab, Lord Oberon decreed that no member of the Third Race may interfere in the affairs of mortals. Though many members of the Third Race (including Oberon himself on occasion) have found ways to bend that particular rule. He is also the father of Merlin by a mortal noblewoman.
Oberon at GargWiki