The cover art on the original 1st Edition DMG is an iconic image that may well have led to some of the hysteria known as the Satanic Panic. The image, of course, does not represent Satan or anything of the sort. But those who sought to ban Dungeons and Dragons from schools and other places did not see it that way. The image looked like something Satanic therefore it was.
What is actually represented was the fabled City of Brass. The Efreeti on the cover towers high above a wizard and a fighter while holding a lovely lady who is probably a thief. At the time of the publication of the DMG there were no adventures that I know of involving the City of Brass but clearly the artist had ideas about such. Later there were some third party offerings involving this place.
The back cover of the DMG shows the City of Brass in the distance beyond a sea of fire (or perhaps lava) with a boat sailing in the foreground. The guard captain has used his magical powers to enlarge himself. It is his task to guard the entrance into the city.
The City of Brass is the center of the Efreeti world. It is set on the elemental plane of fire. The city floats on this plane in a sea of fire or lava. The city is constructed of brass. It is ruled by a great Sultan of the Efreet. It is ruled with an iron fist. It is known as the oldest city wall in existence on any plane. It is a hub for trade on the various planes of existence and is visited by many planar travelers.
I had the pleasure of seeing the original painting that was used on the cover of the DMG at GenCon 50 in Indianapolis. It was painted by David C. Sutherland III.
