Weakness defined him. Crippled and deformed from his birth, his village of Gorgrond was a hellish prison, a miserable place for a runt like him. Orcs lived and were defined by their strength. He could never be a part of that world. He did his best to simply keep out of the way, but he was always being discovered and beaten. He hated them. Bitterness was his food and poison his drink. He had not a single drop of ambition within himself, except to live through the present day into the next. Not that anything awaiting him the following day would be any different from the last.
The mutterings about him and his appearance, his existence continued, until one day the warriors decided to kill him and be rid of him. The village shaman was quick to intervene and instead told Gul'dan to seek out the resting place of the elements, as he had such incredible potential. He was cast out by the chieftain when he slapped the kind hand away.
And so, sustained only by his bitterness and hatred, Gul'dan left to never return. But after a long time of miserable struggle, he decided that he should seek the place the shaman had spoken of. Better to die there than alone in the forsaken wilderness. Dragging himself to the place, he cried out to the elements and offered himself in service to the one who could end his misery. He was approached… and denied. His anger was all too understandable, but in the absence of the familiar, something whispered to him. It offered him power, in exchange for a pledge. The voice spoke to him, of how it needed him, and in return for becoming a harbinger of this being's fury, he would gain much more than the elements could give him. He would be weak no longer, for he would possess power.
Gul'dan returned unto his birthplace, but a changed being, one capable of ensuring that no one would truly know he was, for he razed the place to the ground and killed everyone. None could ever identify the vengeful orc, which was in perfect accordance with his wishes.