When my brother introduced me to AD&D, he lended me the campaign materials he had collected. These consisted of the old 2nd Edition Greyhawk Boxed sets, accompanied by Sargent-era sourcebooks. One of those was Rary the Traitor.
At the time, I didn't "get" Rary. A powerful wizard who for no reason at all betrayed his friends and allies, even murdering two of them and setting up his own empire for the evulz? No. Sure, the World of Greyhawk is filled with megalomaniacal villains, but at least Iuz the Old and the Scarlet Brotherhood were interesting. Rary was just... lame, I guess.
Until I discovered the amount of lore produced for the Living Greyhawk storyline Blight On Bright Sands. Suddenly, Rary became a well-intentioned extremist. His nemeses misguided. The goal of the story arc, salvation for an ancient kingdom and thwarting the machinations of a dark god.
Yesterday, I mentioned that my next campaign must be set in the Flanaess. Now, I have my master villain and my sandbox.