During the Apostle John's revelation of Jesus (as recorded in the Book of Revelation), John saw the seven angels who stand before God who were given the seven trumpets of the Trumpet Judgements and saw that they were prepared to sound them. After witnessing the first four trumpet blasts, John saw the fifth angel sound his trumpet. He saw a star that had fallen from to the earth from the sky. This star was given the key to the shaft of the Abyss. The star opened the Abyss; and when it did, John reported smoke rising from the Abyss similar to smoke from a gigantic furnace. The sun and sky were darkened by this smoke.
Out of the smoke locusts came dome on the earth to harm only those who didn't have the seal of God on their foreheads. They were not allowed to kill them, but to torture them for five months. During those days, people won't be able to die despite their great desire to die. These locusts had as a king over them the angel of the Abyss whose name is Abaddon in the Hebrew language and Apollyon in the Greek language.
Abaddon is translation of the Greek word Ἀβαδδών (Abaddōn), which in turn is the Greek transliteration of the Hebrew word אֲבַדּוֹן (ăbaddôwn). אֲבַדּוֹן means "destruction" and comes from the Hebrew root word אָבַד (âbad), which means to wander away or, by implication, to perish. Apollyon is the translation of the Greek word Ἀπολλύων (Apollyōn). Ἀπολλύων means "a destroyer".