Mundus was once the ruler of the Underworld Two Millennia ago. He ruled the Demonic Realm for two long and wished to expand his rule to the Human Realm but was stopped by the most powerful Warrior in the Demonic Realm; Dark Knight Sparda. Mundus defeat caused him to slip from existance for the rest of eternity.
Two millennia ago, the Devil Prince Mundus was born into the depths of the Demon World and quickly rose to power. He ruled for an eternity but wished to control more and planned to lead an assault on the Human World.
But Sparda, one of his chief generals awoke to justice and single-handedly defeat both Mundus and his armies. After Sparda sealed the main gate to the Human World and passed through, Mundus released Pandora's Box in order to personfy the Seven Sins within the Human World to continue Demonic Conquest. In his last effort Mundus finnaly slipped from Existance.