A malevolent pagan lord in the Serbo-Russian Povest’ o Tryshchane.
He was known to greet cordially any knight who arrived at his island. At night, however, the Foul Heathen would viciously torture him. Tristan learned of these customs and traveled to the Foul Heathen’s island. When the Foul Heathen discovered the identity of his visitor, he did not enforce the custom.
Later, he reconsidered, and had his knights seize Tristan, who was unarmed. Palamedes happened by and gave Tristan a sword. The two knights together slew all of the Foul Heathen’s warriors. The Foul Heathen himself escaped by fleeing into a church.
Source
Povest’ o Tryshchane | c. 1580