In FO 220, Herumor and his The New Shadow Cult, who worshiped the two Dark Powers, Melkor/Morgoth, and Sauron fought against Eldarion and the Reunited Kingdom. These events were told in the unfinished tale known as "The New Shadow", Tolkien wrote about thirty pages of this story but there was no evil power left, for all of Melkor's power was extinguished in the First Age and all of Sauron's in the Third Age. It is not known what race he was. He could have been a Man but that was never established, as the story was never finished.
Herumor is a Quenyan word that meant 'Black lord' or 'Dark lord'.