Ulthalesh

Ulthalesh was a nathrezim who rose to take control of the prison dimension of Mardum, where the titan Sargeras imprisoned his defeated demon foes in the ages prior to him becoming the Dark Titan. The dreadlord ruled the planet with an iron fist, plotting for the day when he would exact his vengeance against Sargeras. When the titan later returned and shattered Mardum to recruit forces for the Burning Legion, scores of demons refused to join him and instead rallied around Ulthalesh. In answer to the challenge, Sargeras forged a great felsteel scythe from the fires of Mardum's destruction and used it to harvest the souls of the rebellious demons, trapping them in a new prison. Ulthalesh, strongest of will, was the last to be devoured. Sargeras named the weapon Ulthalesh after the dreadlord who had opposed him.

Over the ages, the Dark Titan bestowed the blade on nathrezim, doomlords and even demigods, only to see their spirits be devoured by the scythe as they fell. Over the wailing of souls trapped within the weapon, the titan could hear Ulthalesh's grim laughter. Sargeras would eventually give the scythe to an eredar named Sataiel, who used it to drain the life from the inhabitants of the land later called Deadwind Pass, creating a massive crater filled with roiling magical energies in the process. Sataiel knew that this newly-created magical nexus was even more potent than the weapon she wielded, and also knew that she had to inform Sargeras, but Ulthalesh, whispering to her from within the scythe, urged her not to, saying that one day the two of them would be powerful enough to challenge the Dark Titan. When Sargeras learned of Sataiel's betrayal, he manipulated the Guardian of Tirisfal, a human named Scavell, into hunting her down. Scavell killed the eredar with her own weapon, which devoured her soul as it did so many before. Years later, Sargeras--now possessing the Guardian Medivh--sent the Dark Riders to find the scythe in order to deny Ulthalesh any further opportunities to gain more power through finding new wielders.

According to A Hypothetical Examination of the Legion's Weaknesses, a tome outlawed and deemed apocryphal by the Legion, the scythe is one of the few things in the universe that Sargeras fears, and Ulthalesh has been playing his game with the Dark Titan for millennia. He knows the meaning of patience. Khadgar also believes that Ulthalesh still hopes one day to slay Sargeras.