Gul'dan , also called Gul'dan the Terrible, the Fel Master, and the Lord of Eyes, is a very powerful ork Dark Psyker or Warlock. He is one of the few surviving ork magi left over from the UNSC bombardment of Orsinium. Many of the orks allied with Gul'dan when he formed the bloodthirsty, anti-humanity klan called the Fel Horde.
He struck a deal with the evil lord of the The Burning Legion, Kil'jaeden. A pact where Gul'dan was given tremendous dark power, in exchange for total loyalty to the demonic Legion. Accepting this pact, Gul'dan gained incredible dark powers. He appointed the feared Blackhand the Destroyer to command the military of the Fel Horde. To enforce his own agenda, he created the insidious Shadow Council, which runs the orkish hordes behind the curtains.
Gul'dan and his Fel Horde began the Great Devastation when he and his Jinyu ally, Wise Mari, opened a massive Dark Portal through which the demonic Burning Legion poured through onto Earth.
Almost nothing is known about Gul'dan prior to the events leading up to the Great Devastation.
It is known that he is an older Ork, growing a scraggly white beard and wrinkled skin. It is known that he was a very powerful psyker, even before Kil'jaeden spoke to him. Psykers are also born into the Orkish people, not trained or taught. So therefore, it is known that he was alive long before the bombing of Orsinium, and may have even been recruited into a WAAAGH under some Warboss. Due to the fact that he is psyker, it is believed that he was discriminated against and was treated as lesser by the other orks. However, it is known that he had one true ally amongst the orks, a mighty and bloodthirsty ork known as Blackhand, his adopted son.
When the bombing occurred, Gul'dan and some of his former allies, including Blackhand, wandered around the continent, finding mass graves of orks and bringing them back to life. Other Psykers did this too, but Gul'dan was the most powerful and brilliant of them all. Kil'jaeden sensed this, and contacted the ork. He offered Gul'dan a deal, take control of the orks, have them open a Dark Portal, and destroy anyone in their way. The demon lord offered in return limitless power. Gul'dan eagerly accepted, became empowered by demonic magics, and becoming a Dark Psyker, the first of his kind. In secret, he also gathered like-minded ork Psykers, offering them the powers of a warlock. These exceptionally power-hungry orks agreed, and together, became the sinister Shadow Council, made to rule the orks from behind the scenes. Gul'dan then began to seize control of all the orkish people.
He looked for one who would function as a puppet to the Council. He recruited Boss Krolag to be the face of the new leadership, offering him wealth and power. Krolag reluctantly agreed, suspicious of this dark psyker. They together recruited the fractured ork people, uniting them together once again through both brutality and cunning. Once they were large enough to launch an assault upon the nations of Velous and Terra, Gul'dan ordered the invasion of Argopotamia once again. This officially began the Great Devastation.
Gul'dan and the Shadow Council oversaw Krolag's invasion, which was largely successful; the Sergals did not expect an invasion and so were taken by surprise, and added to that, the orks were angry and stronger than ever. With all these together, the orks were able to take over a large chunk of Northwestern Argopotamia. However, things took a strange turn when Krolag suddenly betrayed Gul'dan, with the intention of wrestling control of the Fel Horde back into his own hands, and restoring the proper orkish legacy. However, Gul'dan anticipated this, and set his contingency plan into motion. The ork warlock feigned surrender, which allowed him to deceive Krolag into a sense of victory, before wounding the orkish warlord and, much to the horror of the soldiers nearby, drained Krolag's soul and life essence, leaving him a decayed husk.
Gul'dan then presented his ultimatum, that any who challenged him would be slowly and painfully destroyed like Krolag. He asked for another mighty ork to take Krolag's place as the Fel Horde's warlord. The one who accepted this invitation was none other than Blackhand the Destroyer, a titanic orkish warlord clad terrifying black armor. Blackhand swore allegiance to the dark psyker, and vowed to fight and die in Gul'dan's service. Pleased with this, and more than willing to trust his friend Blackhand, Gul'dan gave the massive ork the title of Warlord of the Fel Horde, and from there, the orks continued their work in dismantling the nations of Velous.