Herumor was a Black Númenórean who lived in the late Second Age. After the Downfall of Númenor he, along with Fuinur, rose to power among the Haradrim and served Sauron.
Herumor means "Black Lord" in Quenya (from heru = "lord" and morë = "dark").
Other Versions of the Legendarium
In the defunct Middle-earth Role Playing game from the 1980s, Herumor is given an extended history. Fuinur is then his older brother. Tolkien, however, had nothing to do with writing this history.