Who is the "angel of the abyss", and why so called?

At Revelation 9:11, however, the word “Abaddon” is used as the name of “the angel of the abyss.” The corresponding Greek name Apollyon means “Destroyer.” In the 19th century there were efforts made to show that this text prophetically applied to individuals such as Emperor Vespasian, Muhammad, and even Napoleon, and the angel was generally regarded as “satanic.” It should be noted, however, that at Revelation 20:1-3 the angel having “the key of the abyss” is shown to be God’s representative from heaven, and rather than being “satanic,” he binds and hurls Satan into the abyss. Commenting on Revelation 9:11, The Interpreter’s Bible says: “Abaddon, however, is an angel not of Satan but of God, performing his work of destruction at God’s bidding.” jw.org