Ghazghkull Mag Uruk Thraka (usually shortened to Ghazghkull Thraka) is a fictional character from the table top miniature game Warhammer 40,000. He featured heavily in the Armageddon campaigns in which he led a huge Ork horde to try to take the planet. Every campaign in Armageddon also features his nemesis Commissar Yarrick.
Ghazghkull started off as a common Ork of the Goff Klan, on the world of Urk. During a raid, Ghazghkull suffered extensive brain damage from a bolter round to the head. He was tended to by an Ork 'Painboy' known as 'Mad Dok' Grotsnik, who used a bionic device made from adamantium to replace Ghazghkull's cerebellum. Ever since that operation, (although it is unknown if it was because the implant triggered latent psychic powers, or Ghazghkull was just delusional), Ghazghkull began to claim that he was the recipient of visions from the Ork gods, Gork and Mork.
From this point, Ghazghkull rose through the Ork power structure in an ascent that has been described as "meteoric". His strength and courage earned him the respect of other Orks. Ghazghkull also possessed something most Orks lacked - vision. His speeches concerned the Orks' mission to conquer the galaxy. He granted the Orks a sense of unity and purpose (as much as these words can be used to describe Orks and their actions).
At the time Ghazghkull reached the peak of his influence on the world of Urk, the star the world orbited began to show signs of entering the final stages of its life cycle. Ghazghkull claimed that this was a sign from Gork, proclaiming that it was time to launch a great Waaagh!. The Orks of Urk were given a choice: Follow Ghazghkull, or die.
They followed Ghazghkull to an Ork, wanting to claim the galaxy or die in the attempt. The first system to be attacked by the Waaagh! was Armageddon, creating a massive conflict that would come to be known in the Imperium as the Second War for Armageddon. Many chapters of Space Marines, along with the Imperial Guard, were all called on to stop the orks' bloody warpath. Despite initial successes, Ghazghkull was defeated, and retreated from the system.
A notable effect of this invasion resulted in Ghazghkull earning the wrath of Commissar Yarrick, who dedicated his efforts after the Second War to hunting down Ghazghkull, with little success.