”Rend dares make such grand claims because of the protection he is afford by the black flight.”
Warchief Rend Blackhand
was the son of Blackhand the Destroyer, Warchief of the Dark Horde, chieftain of the Blackrock and Black Tooth Grin clans. He had a long running dispute with Thrall over who is the true Warchief of the Horde. In canon, he's also the player character for the Orc Campaign in WarCraft II: Tides of Darkness.
Rend and his brother, Maim, fought under the command of their father, Warchief Blackhand, against the draenei, and then against the humans of the Kingdom of Azeroth during the First War. Following Blackhand's assassination and the ascendency of Orgrim Doomhammer to Warchief of the Horde and chieftain of the Blackrock Clan, they were quick to gather their most loyal followers, and form their own clan, the Black Tooth Grin. Although they distrusted Orgrim for having killed their father, and regularly questioned his orders, they served him loyally throughout the war.
Following the defeat of the Orcish Horde at the end of the Second War, Rend and Maim went into hiding, and managed to avoid capture by the Alliance. They eventually made their way back to Blackrock Spire, were they took control of the remnants of the Blackrock clan. Together, they served as co-chiefs of both the Blackrock and Black Tooth Grin clans. However, as both their clans had been weakened considerably by the battles of the Second War, the Dark Iron Dwarves saw this as their opportunity to reclaim the upper levels of Blackrock Spire from the orcs.
The two were later approached by Teron Gorefiend
who had been sent by Ner'zhul to recruit them into his Horde, as well as secure the support of the Dragonmaw Clan, who was still loyal to Rend and Maim. The two brothers had no interest in Ner'zhul's offer, and sent Teron on his way. Teron would later encounter Deathwing, who leant Ner'zhul the support of the Black Dragonflight, and sent his son, Nefarian, the take control of Blackrock Spire. While Rend and Maim had no interest in joining Ner'zhul, they were quick to accept the support of Nefarian and his black dragons. With their new allies, they quickly turned the tides against the Dark Iron Dwarves, sending them back to the depths of Blackrock Mountain. Tragically, however, Maim was killed in this endeavour, leaving Rend as sole ruler of the Dark Horde.
Rend continued to build up his forces, and maintained the alliances of the Old Horde, retaining the support of the Amani trolls and several ogre tribes. However, his continued boasting of being the true Warchief of the Horde, and the growing threat he posed to the Horde should he decide to prove his claim through war, led Thrall to send a group of adventurers to assassinate Rend, and bring his head back as proof of his demise. They did just that.
While the Dark Horde remained united following the death of Rend, they were ultimately displaced from Upper Blackrock Spire by the Ironmarch, the Iron Horde's expeditionary force sent to Azeroth. As a result, Rend has been removed from the game. He and his brother do not appear to have alternate past counterpart in the Iron Horde's Draenor. Despite rumours to contrary, Rend never traveled to Outland, never became a Fel Orc, or served in Magtheridon's army alongside his brother Maim, and he was never killed by the Illidari. That was a different Rend and Maim.