Iuz the Evil. The Old One. Old Wicked. The cambion son of Graz'zt and Iggwilv rules a broad swath of the Flanaess, his Empire bearing his name. He is the scourge of Greyhawk.
A good villain inspires an adventure. A great villain inspires a campaign.
I turned to the Greyhawk setting in 1992, when I first began thinking about running DnD. Several of my friends had read some portion of Forgotten Realms novels and I didn't want to feel ignorant as a DungeonMaster. But what made me decide on Greyawk was the cover for Iuz the Evil.
For me, Iuz is the archetypal villain for DnD and the benchmark that I compare all of my villainous creations. Gary, I can't thank you enough.