Garatharaxxis

A champion of the Nathrezim, Garatharxxis the One-Horned Lord enacted a reign of terror against the Horde's forces in the early days of Sylvanas Windrunner's reign. Targeting those he believed were meant to exist only as minions of the Burning Legion, his manipulations chiefly targeted the undead of the Rotgarde and the orcs of the Hand of Conquest.
Whole villages - such as the sleepy Forsaken town of Grimsburg - were said to vanish in the wake of his dark designs, with his tendrils said to extend even as far as distant Pandaria. He is also said to have slain the then-leader of the Hand of Conquest Grog'kash the Lesser - an hero of some reknown - during an attempt to dominate both the grunt company and a great horde of local centaur into his dark service. It is said that at some point during this time his schemes were briefly inconvenienced by the sailor-turned-warrior, Benjamin Buckles, who managed to land a single blow against the devilish overlord, shattered one of his horns.

In the end, his plans were thwarted by the Burning Legion's downfall with his flagship the Aruspexis crashing over Stonetalon and accidentally unearthing a power even a dreadlord could not take lightly - with a fragment of Soggothian power taking root in the wreckage and singing into reality a thick of blasphemous darkwood across the mountains. Though this threat was ended, the nathrezim was nowhere to be found for several months, resurfacing only to enact his final ploy.
The Garatharaxxian endgame took place only months before the start of the Fourth War, with the dreadlord bringing Grog'kash back as a nigh-invincible champion styled after the first death knights and staking a claim to the ruins of the Shadowfang Keep, where a ritual took place attempting to link the material world to some vile and unknowable plane of reality. There, the Rotgarde and Hand of Conquest fought side by side to defeat a great army of demons - known as the Garatharaxxian Remnant - before confronting the One-Horned Lord personally.
A costly battle ensued, with the mortal forces kept on the back foot by the terrible power of the nathrezim and the unholy might of his saronite-wreathed champion. In the end, the tide turned only at terrible cost - with the superintendent of the 13th, a goblin known only as Salty Seadog, gave his life to detonate an explosive charged that shattered the corrupted orc warlord's physical form and freed his spirit, allowing it to join the assault on Garatharaxxis.
With his champion's betrayal, the dreadlord's defences were compromised and he soon found himself overwhelmed - with the assault being led by heroes such as the infamous Hangart 'Wrathrib' Helmar - and slain on the cusp of a gate to the Twisting Nether, his flesh destroyed and his broken and powerless spirit was doomed to wander Azeroth...