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. (Rev 9:11 KJV)
καὶ ἔχουσιν ἐφ᾽ αὐτῶν βασιλέα τὸν ἄγγελον τῆς ἀβύσσου ὄνομα αὐτῷ Ἑβραϊστὶ Ἀβαδδὼν καὶ ἐν τῇ Ἑλληνικῇ ὄνομα ἔχει Ἀπολλύων (Rev 9:11 Textus Receptus)
In Biblical poetry (Job 26:6; Proverbs 15:11), it comes to mean "place of destruction", or the realm of the dead, and is associated with Sheol. Abaddon is also one of the compartments of Gehenna.
In Revelation 9:11, it is personified as the demon Abaddon, "Angel of the Abyss", rendered in Greek as Apollyon; and he is described as king of the locusts which rose at the sounding of the fifth trumpet. In like manner, in Rev. 6:8, Hades is personified following after death to conquer the fourth part of the earth.
Abaddon is one of the infernal names used in Satanism, and is first in the list—only as it comes first alphabetically—and means "the destroyer."
→ Prophecy In The News Special On Apollyon Rising 2012