King Xerxes is the mighty king of Persia and rival of Leonidas from the movie 300. He currently appears as a non-playable character in Smash Bros. Lawl.
Role in the Subspace Emissary
He is hired by Ganondorf or the Ancient Minister to attack Sparta with Robotnik. When Leonidas is busy chasing Robotnik out of the doomed city, Xerxes hides in a cliff and summons his Persian Army to ambush Leonidas. It proved futile, and Xerxes retreats to create more schemes.
In The Persian Forest, Xerxes sends his Persian Army to set the woods ablaze, as he knew that Leonidas is busy looking for Robotnik. In case Leonidas got through the scorched forest, Xerxes has another ambush of Persian soldiers, as well as Robotnik's badniks, waiting for him at the end of the forest. Neither Xerxes nor Robotnik expects Leonidas's alliance with King Harkinian, though. Xerxes tries to trophy the Sparta King with a Dark Cannon, but Leonidas knocked it away with his spear, forcing the partners in crime to retreat. (The Dark Cannon was later found by Gaston.)
Xerxes and Robotnik are sent by Ganondorf again when the Irate Gamer required assistance to chase out the Nostalgia Critic, Tommy Wiseau, and Madotsuki. The villainous duo sends the mooks for another ambush.