The city of Orgrimmar, home to orcs and trolls, and the main hub for Horde players post-Cataclysm is a sprawling place. Like Stormwind, it has undergone a few changes since Deathwing emerged from the earth.
The Orgrimmar gates were the canon location for the head of Nefarian, another one of Deathwing's children, and brother of Onyxia. Like in Stormwind, Deathwing didn't take kindly to his son's head being used as a trophy, so he torched the city and took it back.
The old ruler of Orgrimmar was Thrall, the Horde Warchief, and main lore character for the Horde.
He went from a slave at an orc internment camp to ruler of the Horde. After the Cataclysm, he rushes off to protect the world from being ripped apart by the damage, and he leaves the brash young Garrosh Hellscream, who jogs with a fridge on his back, in charge.