Azzinoth

The fearsome demon called Azzinoth was a doomguard commander of the Burning Legion during the War of the Ancients before the Great Sundering. He met his end, however, when he came upon Illidan Stormrage.

Illidan slew Azzinoth, and took his weapons, a pair of vicious warglaives called the blades of Azzinoth. Over the millennia, Illidan grew more and more adept with the demonic weapons, and likely became more proficient with them than their original owner. He carries them still.

In his duel with Arthas, Illidan mentions that Azzinoth was a "powerful demon captain".

Related
All of these drop from Illidan Stormrage.

The fire elementals Flame of Azzinoth and Ember of Azzinoth, which are spawned from the weapons, are somehow related to Azzinoth as well.