Eric Morden was just another underling under the orders of the Brain in the Brotherhood of Evil, essentially a grunt, tasked with working several machines; he once stole one of the Chief's lunar exploration droids,Rog. However, he, the Brain and Monsieur Mallah had a fallout of some sort, and Morden preferred to flee rather than face the wrath of the Brain. Both villains threatened to kill Morden if he returned, so he hid for years in Paraguay.
Morden was already somewhat unstable, and contacted a Nazi scientist and was exposed to a device called the White Room, which drove him irredeemably insane and converted his body into a mass of living virtuality that could drain the sanity from other humans. The experience also convinced him the universe was "a drooling idiot with no fashion sense". Calling himself the man of the twenty-first century, the first true virtual man, he rechristened himself Mister Nobody and organized the rebirth of a Brotherhood that shared his ideals. Because of this, he chose not to restart the Brotherhood of Evil and instead initiated the Brotherhood of Dada, a group of lunatics that followed Morden's ideas to change the world.
His first plan was to steal a magical painting and feed the city of Paris to it; he suceeded, and the entire city was thrown into an alternate universe from where the Doom Patrol managed to recover and restore it. However, many members of Nobody's Brotherhood chose to remain in the insane alternate realm. Mister Nobody escaped, however, and enacted a second plan to change the world: he stole Albert Hoffman's bicycle and used its lysergic resonance to power his own presidential campaign in the U.S.A. . The U.S. government, unwilling to see a madman like Nobody step up to the Presidency, sent a similarly insane agent, John Dandy, who used one of the faces floating around him on Nobody, stripping him of his powers and impaling him upon a broken pole. Morden faded to nothingness after the attack.
However, he has resurfaced in the Trinity series, as a candidate for the Dark Arcana's The Fool and as a part of the Final Battle for the Arcana in Metropolis.