Gorehowl is the epic two-handed axe that once belonged to the orcish warrior and former chieftain of the Warsong Clan, Grom Hellscream and now belongs to Garrosh Hellscream, his son. It drops from Prince Malchezaar in Karazhan.
Hellscream was the first to partake of the Blood of Mannoroth, eventually coming to regret it. When Thrall met him, it was clear to him that Grom had the means by which to liberate his lethargic brothers and sisters.
During the second coming of the Burning Legion, Hellscream took his axe to the pit lord Mannoroth after Thrall was beat into unconsciousness. With a single blow, Hellscream cleaved his adversary's weapon in two and slew Mannoroth. Hellscream perished shortly afterwards, but he had managed to break the curse over his people, freeing their souls and spirits from the demonic curse forever.
Gorehowl somehow wound up in the hands of Prince Malchezaar after Grom's death.
In Orgrimmar, Thrall presented Gorehowl to Garrosh as a gift. It is seen in the picture named "Gift of Gorehowl" by Raneman.
This section concerns content exclusive to the Warcraft RPG, and thus is not necessarily canon.
Grom Hellscream’s axe has a heavy blade that is notched and stained, with sharp, wicked curves. Small holes dot the blade near the handle; when the wielder swings the axe, air whistles through these holes. The sound keens over the battlefield, magically strengthened and imbued with otherworldly power. Gorehowl is one of Azeroth's most feared and notorious weapons.
A weapon similar to Gorehowl has also been depicted in the trading card for Blademistress Lyss.