He is the father of the modern Horde. His name became the name of the great city built by the orcs. He found in the son of his oldest friend a protegé who would lead his people, and he passed his family's greatest treasure down to ensure that prophecy was satisfied. To his people, he was one who never forsook them. No attempts to run away from the consequences of their actions, no dissembling -- simply forthright, pragmatic action. Alone of the Blackrock Clan, he refused the taint of the demon blood, yet found himself marked by it as it spread through his people. Called the Backstabber because he killed his direct superior, Blackhand the Destroyer, he ruled the Horde until its final defeat at Blackrock Mountain.
To his enemies, he was death. He beheaded his own chieftain and seized power in one brutal moment, crushing any opposition by the swift assassination of his enemies.He destroyed Stormwind and nearly brought down Lordaeron. He killed the majority of the warlocks of the Shadow Council and removed the position of Warchief from the role of a puppet ruler, leading the Horde in truth. He asked for no quarter and gave none. He countenanced the capture and forced breeding of the dragon queen Alexstrasza and her consort Tyranastrasz, using the juvenile dragons as mounts. He allowed Gul'dan to live, even though he suspected treachery, because the old warlock promised him a weapon that could counter the magics of the humans. He was never one to put his conscience ahead of what he saw as his duty; even as he suspected the orcs were being lied to and manipulated, he took part in the slaughter of the draenei. In the end, his own pragmatism cost him the victory in the Second War, as the treacherous Gul'dan proved that placing victory above all sometimes means giving someone too much rope -- Gul'dan's betrayal of the Horde in its moment of victory effectively destroyed all of the hard work of its Warchief.
Orgrim Doomhammer, last of the Doomhammer line, Warchief of the Horde, chief of the Blackrock, was an orc, give him all in all. You shall not look upon his like again.