History:
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.
It should also be noted that Gorehowl is the weapon which slew the night elf demigod Cenarius.
Gorehowl somehow wound up in the hands of Prince Malchezaar after Grom's death.
In Orgrimmar, Thrall presented Gorehowl to Garrosh as a gift
http://www.wowwiki.com/Gorehowl
Keywords:
Gorehowl, Hellscream, Garrosh, Grom