Pete took out a bunch of his old D&D books, here are some relevant quotes:
MM2:
I’m paraphrasing, here, “He was winning the war in the Abyss against Orcus and Demogorgon when he was summoned by a mighty magic-user and pulled to the prime material plane. Cool. That fits right into the game we’re in.”
“Graz’zt is the handsomest of the demon rulers, at least by human standards. He appears as a huge, good-looking man, although his skin is shining black and his eyes are glowing green. Graz’zt is six fingered and six toed.”
The 3.0 Manual of the Planes is a nifty book. I especially like the 3-line descriptions of each plane:
“It is an infinity of clutching horror.
It is home to demons.
It is where morality crumbles and ethics perish.”
Githyanki Diaspora 
Interesting.
The last poster reminds me that it’s hard for me to see Graz’zt outside of the context of Greyhawk, whereas Orcus or Demogorgon seem more catholic *rimshot*
Did not Pope Cuthbert warn us of Orcus’ undead influence in our day-to-day lives?
There’s a great illo of Graz’zt in the old Lost Caverns of Tsojcanth. but my Google Image-fu isn’t finding it. If you can hunt down a copy, that old adventure is great. One book of adventure, one book with tons of monsters and great art.
This one?
TIME WARP: Nope, it’s this one (though this one’s a pretty bad scan): http://www.canonfire.com/wiki/images/1/1d/Grazzt02.jpg
Thanks!