Abaddon

The Hebrew term Abaddon (Hebrew: אֲבַדּוֹן‎ ’Ăḇaddōn means "the Doom", "destruction", or "devastation"), and its Greek equivalent Apollyon (Greek: Ἀπολλύων, Apollýōn) appear in the Bible as both a place of destruction and an angel of the abyss. In the Hebrew Bible, abaddonis used with reference to a bottomless pit, often appearing alongside the place שְׁאוֹל (Sheol), meaning the realm of the dead.

Myths & Legends
In the New Testament Book of Revelation, an angel called Abaddon is described as the king of an army of locusts; his name is first transcribed in Greek (Revelation 9:11—"whose name in Hebrew is Abaddon, the Angel of Death.") as Ἀβαδδὼν, and then translated ("which in Greek means the Destroyer", Ἀπολλύων, Apollyon)).

Hebrew Bible
The term abaddon appears six times in the Masoretic text of the Hebrew Bible; abaddon means destruction or "place of destruction", or the realm of the dead, and is accompanied by Sheol.
 * Job 26:6: the grave (Sheol) is naked before Him, and destruction (Abaddon) has no covering.
 * Job 28:22: destruction (Abaddon) and death say..
 * Job 31:12: it is a fire that consumes to destruction (Abaddon)...
 * Psalm 88:11: Shall thy loving kindness be declared in the grave (Sheol) or thy faithfulness in destruction (Abaddon)?
 * Proverbs 15:11: Hell (Sheol) and Destruction (Abaddon) are before the LORD, how much more the hearts of the children of men?
 * Proverbs 27:20: Hell (Sheol) and Destruction (Abaddon) are never full; so the eyes of man are never satisfied. (KJV, 1611)

Second Temple era texts
The text of the Thanksgiving Hymns—which was found in the Dead Sea Scrolls—tells of "the Sheol of Abaddon" and of the "torrents of Belial [that] burst into Abaddon". The Biblical Antiquities (misattributed to Philo) mentions Abaddon as a place (destruction) rather than an individual. Abaddon is also one of the compartments of Gehenna. By extension, it can mean an underworld abode of lost souls, or Gehenna.

Rabbinical literature
In some legends, Abaddon is identified as a realm where the damned lie in fire and snow, one of the places in Gehenna that Moses visited.

New Testament
The Christian scriptures contain the first known depiction of Abaddon as an individual entity instead of a place.

Revelation 9:11

A king, the angel of the bottomless pit; whose name in Hebrew is Abaddon, and in Greek Apollyon; in Latin Exterminans.

Douay-Rheims Bible

In Revelation 9:11, Abaddon is described as "Destroyer",  the angel of the abyss,[6 ] and as the king of a plague of locusts resembling horses with crowned human faces, women's hair, lions' teeth, wings, iron breast-plates, and a tail with a scorpion's stinger that torments for five months anyone who does not have the seal of God on their foreheads.

the symbolism of Revelation 9:11 leaves the identity of Abaddon open to interpretation. Protestant commentator Matthew Henry (1708) believed Abaddon to be the Antichrist,  whereas the Jamieson-Fausset-Brown Commentary (1871) and Henry H. Halley (1922) identified the angel as Satan. Latter-Day Saints believe that the use of "Abaddon" in Revelation 9 refers to the devil.

In contrast, the Methodist publication The Interpreter's Bible states: "Abaddon, however, is an angel not of Satan but of God, performing his work of destruction at God's bidding", citing the context at Revelation chapter 20, verses 1 through 3. Jehovah's Witnesses also cite Revelation 20:1-3 where the angel having "the key of the abyss" is actually shown to be a representative of God, concluding that "Abaddon" is another name for Jesus after his resurrection.

Gnostic texts
In the 3rd century Acts of Thomas, Abaddon is the name of a demon, or the devil himself.

Abaddon is given particularly important roles in two sources, a homily entitled "The Enthronement of Abbaton" by pseudo-Timothy of Alexandria, and the Apocalypse of Bartholomew. In the homily by Timothy, Abbaton was first named Muriel, and had been given the task by God of collecting the earth that would be used in the creation of Adam. Upon completion of this task, the angel was appointed as a guardian. Everyone, including the angels, demons, and corporeal entities feared him. Abbaton was promised that any who venerated him in life could be saved. Abaddon is also said to have a prominent role in the Last Judgement, as the one who will take the souls to the Valley of Josaphat.[15] He is described in the Apocalypse of Bartholomew as being present in the Tomb of Jesus at the moment of his resurrection.

Etymology
According to the Brown Driver Briggs lexicon, the Hebrew abaddon (Hebrew: אבדון‎; abaddon) is an intensive form of the Semitic root and verb stem abad (אָבַד)  "perish" (transitive "destroy"), which occurs 184 times in the Hebrew Bible. the Septuagint, an early Greek translation of the Hebrew Bible, renders "Abaddon" as "ἀπώλεια",  while the Greek Apollyon comes from apollumi (ἀπόλλυμι), "to destroy". the Greek term Apollyon (Ἀπολλύων, "the destroyer"), is the active participle of apollumi (ἀπόλλυμι, "to destroy"). the Latin Vulgate and the Douay Rheims Bible have additional notes (not present in the Greek text), "in Latin Exterminans", exterminans being the Latin word for "destroyer".