Their origin was in the latter half of the Second Age. Lovers of power over lesser Men, the Númenóreans known as the King's Men became corrupted by Sauron, coming to hate all good peoples. They settled in Middle-earth, mainly in Umbar and surrounding coastal regions: far away from the Elves that lived in Eriador and Rhovanion.
After Sauron's downfall at the beginning of the Third Age, the bloodlines of these Númenórean descendants mixed with other peoples, especially the Haradrim over which they had dominion. During the first millenia of the age, they proved strong enemies of their distant kin the Dúnedain of Gondor, but were permanently scattered when Umbar was taken. Some of them fell directly under Sauron's rule, others returned to Umbar after the Kinstrife of Gondor. They still retained many of the ancient characteristics of the Edain, like their cousins the Dúnedain, although since their blood mixed more with lesser Men than that of the Dúnedain the length of their lives had dwindled to that of lesser Men by the end of the Third Age.