"We'ze gonna stomp da world flat an kill anyfing dat fights back. We'ze da orks, and we was made ta FIGHT an' WIN!!"
Warlord Ghazghkull Mag Uruk Thraka was the last great Warlord of the Orkish WAAAGHs. He was immensely powerful, widely respected, and feared. He was considered to be the greatest ork to have ever lived, outdoing every previous warlord, even Gorgutz 'Ead Unter. Ghazghkull led the mightiest ork WAAAGH ever witnessed during the events of the Ork and Sergal War, one of the most cataclysmic conflicts to ever be waged upon the Sergal race. Thraka was notorious for the genocide he commited since his rise to power, and he is so revered that he was nicknamed "Da Butcha".
The mighty Ghazghkull Thraka was slain at the Battle of Gorgutarn, where he and the WAAAGH Ghazghkull holed up and defended the city from the UNSC and Sergals. Though the orks were successful in defending the city, after about 3 days of fighting through and countless casualties, the combined force stormed Gork'han Hold and slew Ghazghkull, ending his threat to the world and saving countless lives. This act ended the bloody war, and finally brought peace to the nations of Velous. For a time.
Orks don't necessarily keep very good or detailed records of their histories, so much history of individual orks are virtually nonexistent until one rises to power. Ghazghkull is such an ork, and records of his life begin during his time serving in WAAAGH Gorgutz.
During the Wasteland Wars, during the time of Warlord Gorgutz 'Ead Unter's rule over the orks, the many different orkish clans were united under the single banner of WAAAGH! Gorgutz, so it goes with all large orkish armies. The ork known as Ghazghkull belonged to the Goffs Klan, one of the largest and most powerful of all the klans, notorious even amongst other orks for their brutality and berserker mentality.
Ghazghkull, during this time period, was a Nob Chief, leading large amounts of orks into combat against their various enemies, be they bandits like the Shrouded Ghosts, or bigger foes like remnants of Malefor's Holy Empire. Ghazghkull was known, rather early on, for his strength and his smarts (for an ork, that is). He was a tower of muscle and rage, often exploding into murderous frenzies and killing virtually everything in his path. The boyz under his command were said to be constantly inspired and blood-hungry in the presence of their leader. This is great testament to the Nob Chief's influence, indeed, the Warlord Gorgutz himself realized this and allowed him to join his "inner circle" of high-ranking advisors. This was composed of a handful of strong, powerful orks who ruled their respective klans and commanded sizable portions of the orkish war efforts - among these klan chiefs was the soon-to-be-Warlord Grimskull. This is about where his influence in WAAAGH! Gorgutz ended. Unfortunately for the orkish people, Warlord Gorgutz was slain on his personal forktress, the "Big Bugger" by the members of Blue Team.
When news of the Warlord's fall reached his "inner circle", the orkish klan chiefs immediately began to lay claim to the title of successor Warlord. In the tradition of all orks, they eventually broke into combat, beating each other down into submission, until one remained to inherit rulership. Following the large scrap of orkish behemoths, there remained only two who remained standing, the mighty Ghazghkull and the cunning Grimskull. The latter, however, came prepared to the assembly, with poisoned claws, designed to incapacitate on contact. In the ensuing battle, Grimskull was initially being battered by the larger, stronger Ghazghkull, but Grimskull only needed one good hit on his foe, which he got. Within a few moments, Ghazghkull fell and begrudgingly admitted defeat, thereby relinquishing his claim on the title of Warlord, which passed to Grimskull.
Warlord Grimskull however, displayed some measure of honor by allowing his defeated foes a place in his own inner circle. The klan chiefs, though still sour about their defeats, were loyal to their new Warlord and followed his orders during the ensuing conflict, the Mythic Dawn War. During this time, the orkish people (Grimskull, namely), sided with the sinister Mythic Dawn cult, seeing the benefits of such a powerful presence on their side. Ghazghkull, however, disagreed wholeheartedly with this decision. He felt that the orkish people should bow to no authority, other than the Twin Gods Gork and Mork. Ghazghkull felt that they should take up arms and battle the Mythic Dawn. Warlord Grimskull, of course, disregarded this sentiment completely. This only added fuel to the fire, however, as within Ghazghkull the ideas of total orkish supremacy and the hatred of all other lifeforms built in his mind. Regardless, he continued to lead his Goffs in combat against the Mythic Dawn's foes, namely the sergals, UNSC, the Equestrians, and Blue Team.