His domain was a small pocket dimension, sandwiched between two universes (both of them infinite stretches of sandwiches, one Ruben, one Cuban).
He made it after he was defeated by a plucky rag-tag group of misfit adventurers, and his goal was to study the multiverse and work out how to avoid losing again.
Unfortunately, all he found was more ways to lose. So many universes had books or weapons that empowered those that touched them, many more with destined heroes, for some reason.
There were ways for evil to win that he found, sure, but they were all so dull.