Han-Gra-Dan is a mysterious historical figure about whom almost nothing is known.
Han-Gra-Dan is described as a Baklunish man with "an intense glare."
In Zagig's Promenade beneath Castle Greyhawk, a statue of Han-Gra-Dan, depicted with his arms raised, is positioned opposite a statue of Slerotin, who seems to share Han-Gra-Dan's glare, observing Han-Gra-Dan with some distaste. This may indicate that Han-Gra-Dan was a Baklunish Mage of Power, some sort of rival of Slerotin's during the Baklunish-Suloise Wars.
The statues in Zagig's Promenade are of people who inspired Zagig at the time of his apotheosis (earlier, discarded heroes had their statues periodically destroyed and replaced with new ones). Evidently, then, Zagig found something admirable enough in Han-Gra-Dan to be worth celebrating.