A people who dwelt in north-eastern Eriador until the middle Third Age. Some, subjects of the Witch-king of Angmar, may have also dwelt near the sources of the Anduin. Their origins are unknown, but they were most probably descended from First Age (Beleriandic) Easterlings. They were declared "evil" by the Dúnedain because of their alliance with Sauron, consolidated in the Dark Years, which they never abandoned.
The Hillmen were subdued by Elendil and Isildur when most of their lands were claimed for Arnor at the end of the Second Age. In 861, Arnor was divided into three kingdoms, and the Hillmen became subjects of the new kingdom of Rhudaur which, over time, they came to dominate, driving out or destroying the remnants of the Dúnedain. When in 1300 the Witch-king established Angmar at the far northern end of the Misty Mountains, many Hillmen in the area flocked to his banner; those who remained in Rhudaur formed an alliance with him against Arthedain and Cardolan (in 1409). Hillmen slew Argeleb, Arthedain's king, in 1356; they remained at war with the western kingdoms thereafter.
The tale of the Hillmen comes to an end in 1975 when, having decimated the forces of Arthedain and Cardolan, the armies of Angmar and Rhudaur were themselves destroyed by Gondor and Lindon (and the Shire).
Other folk to be described as "hillmen" in Tolkien's writings include the regiment of Lamedon sent to the aid of Gondor, and the Dunlendings.