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. A king over them - A supreme head; some think Mohammed, some think Vespasian.
The angel of the bottomless pit - The chief envoy of Satan.
Abaddon - From אבד abad, he destroyed.
Apollyon - From απο, intensive, and ολλυω, to destroy. The meaning is the same both in the Hebrew and Greek.