(portrait of Apollyon from Francis Barrett's The Magus, 1801)
Cornelius Agrippa equated this demon with Abaddon, and placed him as ruler in the lower shadow of the sphere of the planet Venus, which is the Sephirah of Netzach on the Kabbalistic Tree. "The seventh mansion the Furies possess, which are powers of evil, discords, war and devastations, whose prince in the Revelations is called in Greek Apollyon, in Hebrew Abaddon, that is destroying and wasting" (Occult Philosophy, Book 3, Chapter 18). The biblical verse cited by Agrippa is Revelation 9:11, which reads: "And they had a king over them, which is the angel of the bottomless pit, whose name in the Hebrew tongue is Abaddon, but in the Greek tongue hath his name Apollyon."
In the Old Testament the name Abaddon is used for the place of the dead. It literally means destruction or perdition. Apollyon is the Greek equivalent, and may be translated Destroyer.The portrait of Apollyon in Barrett's Magus does not appear particularly furious, but we may assume that the mild aspect of the demon is intended to deceive, and conceals a heart festering with malice and rage.