Revelation 9:11-15

They have as king over them, the angel of the abyss; his name in Hebrew is Abaddon, and in the Greek he has the name Apollyon.

The first woe has passed; behold, two woes are still coming after these things. The Sixth Trumpet: Army from the East

Then the sixth angel sounded, and I heard a voice from the four horns of the golden altar which is before God,

saying 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 prepared for the hour and day and month and year, were released, so that they would kill a third of mankind.