Revelation 9:11
WEB
They have over them as king the angel of the abyss. His name in Hebrew is "Abaddon," and in Greek, he has the name "Apollyon."
KJV
And they had a king over them, which is the angel of the bottomless pit, whose name in the Hebrew tongue is Abaddon, but in the Greek tongue hath his name Apollyon.
Commentary
Commentary