The King of the Faeries was a figure in Irish folklore.
In 2376, Fair Haven resident Michael Sullivan told Katie O'Clare that at nightfall, the King of the Faeries would reclaim nearby Castle O'Dell. Consuming the food of the faeries would land one in their realm forever. (VOY: "Fair Haven")
Oberon, a character in A Midsummer Night's Dream, was King of the Faeries.