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. But they also had more southern ports on the coasts of Belegaer.

After Sauron's downfall at the end of the Second 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. Two of their lords, Herumor and Fuinur fought against the Last Alliance of Elves and Men in 3429 S.A.. In the early Third Age Umbar was one of the strongest enemies of Gondor, although it seems the realm slowly weakened over time:

In those days our bounds were away south beyond the mouths of Anduin, and Umbar, the nearest of their realms, acknowledged our sway. — Damrod of Gondor in The Two Towers, speaking about the time of the Kings.

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.

The Mouth of Sauron, who provoked the army of King Elessar in front of the Black Gate of the Morannon, was a Black Númenórean.