Demogorgon, Prince of Demons: D&D Icons of the Realm

The demon lord is a meld of different forms, with a saurian lower body and clawed, webbed feet, as well as suckered tentacles sprouting from the shoulders of a great apelike torso, surmounted by two hideous simian heads, named Aameul and Hathradiah, both equally mad. Their gaze brings madness and confusion to any who confront it.