Uldor was the youngest son of Ulfang the Black.
Like other Easterling tribes, he was one of the many tribes of Easterlings who entered into the service of the Sons of Fëanor. Serving with Caranthir since 457, he and brothers Ulfast and Ulwarth helped him prepare for war with Morgoth but like the rest of his family they were already secretly allied with him. They agreed to betray Maedhros an his forces to Morgoth in the Nirnaeth Arnoediad by sending a series of false warnings of an attack from Angband from another point. This delayed march of the Eastern Army under Maedhros from joining the rest of the coalition in time for the main battle. He was the leader in the treachery after his father's death and attacked the Eastern Army from their rear with a hidden force of Easterlings. He was slain by Maglor but it was too late his actions helped Morgoth win the battle.