Gul'dan was originally an apprentice to the Orc Shaman Ner'zhul on the planet of Draenor. Gul'dan discovered that Ner'zhul had been secretly trafficking with the demon lord Kil'jaeden, but had been unwilling to fully embrace demonic magic, fearing it would ruin his people. Ner'zhul's apprentice however, had no such scruples. Gul'dan was approached by Kil'jaedan and offered the chance to become a master of warlock magic if he would help corrupt the Orcs. Gul'dan accepted, and immediately began the work of turning the Orcs from a collection of simple shamanistic clans, into an unstoppable and blood thirsty Horde. Gul'dan trained a number of like minded Orcs, whom he named the Shadow Council. The Council was soon using its power and influence to direct almost every aspect of Orc society. He even founded and created his own clan, which was fanatically loyal to him, known as the Stormreaver Clan.
Under Gul'dan's direction, the Orcs murdered every single Draenei they could find on their homeworld. It was also he that initiated the bargain between Mannoroth and the Orc chieftans, which cursed the Orc race with demonic fury and bloodlust.
Eventually, Gul'dan was contacted by the mad sorcerer Medivh, who offered him the promise of godhood, locked away within the Tomb of Sargeras if he would use the Horde to conquer Azeroth. Gul'dan agreed, and with the assistance of the Shadow Council, helped Medivh open the Dark Portal between Azeroth and Draenor. Over the next few years, Gul'dan and his Ogre-Mage apprentice Cho'gall would secretly manipulate the Horde as it rampaged across Azeroth. Even after he lost direct control to Orgrim Doomhammer, he still plotted in secret.
Gul'dan submits
Ultimately, Gul'dan's treachery proved to be the Horde's undoing. On the eve of Doomhammer's attack on Lordaeron's capital, Gul'dan took all the clans loyal to him and sailed south to find the Tomb of Sargeras. With half of his standing forces suddenly gone, Doomhammer was forced to retreat and hunt down the traitorous warlock. This reprieve would ultimately give the Alliance time to regroup and retaliate.
Gul'dan used his power to raise the tomb from the ocean floor. Taking with him his most select followers, Gul'dan cast open the doors and entered. He did not however find the godhood he was hoping for, instead, he was torn to shreds by a swarm of demons that they had unleashed when the tomb was opened.
Gul'Dan's memories survived within the warlock magic of his skull and the runes he painted on the walls of the Tomb. Illidan found the Tomb using Gul'Dan's memories from the Skull, and Maiev found the runes. When the tomb caved in Gul'Dan's final testament was buried, and Illidan ignored Gul'Dan's memories thereafter, burying forever the most evil orc the universe had ever known.
(A fan suggestion is that Illidan's madness and lethargy following the battle with Arthas will lead to Gul'Dan's memories taking precidence, but serious players will allow Blizzard to think up the plot twists...)
The Skull of Gul'dan
Gul'dan
After Gul'dan died, his skull was turned into a channeling totem for demonic energy. The skull was used by Ner'zhul to open portals to other worlds on Draenor, and later by Khadgar to destroy the Dark Portal. After the destruction of the Dark Portal, Khadgar left the skull behind on Draenor in his haste to escape through one of Ner'zhul's rifts. Years later it would appear again on Azeroth, this time used by the Burning Legion to corrupt the forests of Felwood. The skull was eventually destroyed by Illidan Stormrage, who absorbed its power, becoming half Night Elf and half demon.
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