This is a list of all unique monsters in nethack, which appear only once, with the exceptions of the Wizard of Yendor, who reappears occasionally, and the three riders, which resurrect.

The Oracle

“The Wizard of Yendor (also informally known as Rodney) is the guardian of the Book of the Dead...

Wizard of Yendor

“Demogorgon is the most difficult of the demon princes and, indeed, the most difficult monster of...

Demogorgon

“Medusa is a dangerous monster with her own level, which is somewhere in the main Dungeons of...

Medusa

“Vlad the Impaler, V, is a unique vampire notable in that he holds the Candelabrum of Invocation...

Vlad the Impaler

“Asmodeus, &, is the most powerful of the demon princes who is guaranteed to appear in Gehennom...

Asmodeus

“Juiblex is a demon lord whose lair is a swamp. He can engulf and make ill any character he meets...

Juiblex

“Croesus, @, is the rich owner of the Fort Ludios and of all vaults. He resides on a throne in...

Croesus