The primordial Thunder King has returned to fulfill his life's work: rebuilding the dynasty of his monstrous race on the continent of Pandaria.
Even among the mighty mogu of ancient Pandaria, Lei Shen was known as a military prodigy. The son of a warlord, Lei Shen aimed not simply to conquer weaker races, as his forebears had done, but to build a true empire. To do so, he traveled to the mythical Thundering Mountain, where he sought the truth about the forgotten god of the mogu and its powers. What he found was illuminating: the titanic watcher Ra-den, who stood guard over a powerful titan device, the Engine of Nalak'sha. Lei Shen claimed dominion over both; then, with his newly acquired powers, he dubbed himself the Thunder King and established tyrannical rule over Pandaria until the time of his death.
Once the mists parted, revealing Pandaria again to the world, the Zandalari trolls joined with the scattered mogu and resurrected their former leader, who returned to his fortress, the Throne of Thunder. There, with his followers, he began a campaign to crush the pandaren (and their foreign allies among the Alliance and Horde), reclaim the continent, and rebuild his empire of old.