Haomarush is a PvP realm which opened in August 2005. It was originally named Haumarush due to a typo during the realm's creation which was subsequently fixed on a regular weekly maintainence.
Haomarush is part of the Rampage Battlegroup which consists of 13 English-speaking realms.
Haomarush was among the leaders of the last remnants of the demon-worshipping Orcs, all under the rule of Jubei'Thos and the Blackrock clan. Being one of the lesser Blademasters within the clan, Haomarush was given command over a small contingent known as Blackrock Scouts, which he used to survey the area around the Alterac Mountains, where they had constructed a settlement to guard a demon gate. During one of his scouts, however, his troops ran into Arthas, and the dark prince quickly routed and killed them all.
His name is likely a reference to Haohmaru, the main character in the Samurai Spirits series of fighting games.