Dumac (also known as Dumac Dwarf-Orc , and Dumac Dwarfking ) was a Dwemer king, head of the clan in Morrowind (or Resdayn, as it was known back then). He was known to have been in attendance of the coronation of King Gorieus in 1E 461. 
Unbeknownst to him, one of his chief council members, Kagrenac, was working in secret to create a new Dwemer God. The Chimer found this out, and the First Council broke down, and the War of the First Council began.  During the resulting Battle of Red Mountain, Nerevar killed Dumac.