Revelation 9:11-16 NIV
They had as king over them the angel of the Abyss, whose name in Hebrew is Abaddon and in Greek is Apollyon (that is, Destroyer).
The first woe is past; two other woes are yet to come.
The sixth angel sounded his trumpet, and I heard a voice coming from the four horns of the golden altar that is before God. It said to the sixth angel who had the trumpet, “Release the four angels who are bound at the great river Euphrates.” And the four angels who had been kept ready for this very hour and day and month and year were released to kill a third of mankind. The number of the mounted troops was twice ten thousand times ten thousand. I heard their number.
NIV: New International Version