Uldor

In J. R. R. Tolkien's legendarium, the Easterlings of the First Age were Men who lived in the east of Middle-earth, and mostly fought under Morgoth. They are different from the Easterlings of later Ages.

Their first appearance was at the end of the First Age, when in Y.S. 463 some tribes of the Swarthy Men entered Beleriand from Eriador, passing north about the Blue Mountains:

The prime reason for their migrating was the rumour of the wealth and peace of Beleriand as it was during the Siege of Angband, but many Easterlings have journeyed on behalf of Morgoth the Dark Lord, for he had secretly corrupted some tribes and chieftains to his service. The Dwarves of the Blue Mountains had reported to the Elven-lord Maedhros of the coming of Easterlings. Maedhros then decided to make alliance with them in hope of overthrowing Morgoth, and gave them wide lands in Lothlann and in East Beleriand to the south of the March of Maedhros. The most powerful of their chieftains with the greatest followings and authority were Bór and Ulfang; their men were marshalled and trained for war by the Sons of Fëanor, and more of their kinsfolk from Eriador were summoned.

The kinsfolk of the people of Bór that remained in Eriador are said to be the ancestors of the Forodwaith and Lossoth of the Second and Third Ages. The sons of Bór were Borlach, Borlad and Borthand, and his people swore allegiance to Maedhros and his brother Maglor. They remained faithful, and "cheated the hope of Morgoth." During the Nírnaeth Arnoediad they fought on the side of the Eldar and Edain, and after the treachery of Ulfang, the sons of Bór slew Ulfast and Ulwarth, but were themselves wiped out together with all of their folk.

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Wikipedia