Jamieson, Fausset and Brown on Revelation 9:11

11. And--so Syriac. But A, B, and Aleph, omit "and."

had--Greek, "have."

a king ... which is the angel--English Version, agreeing with A, Aleph, reads the (Greek) article before "angel," in which reading we must translate, "They have as king over them the angel," &c. Satan (compare Re 9:1). Omitting the article with B, we must translate, "They have as king an angel," &c.: one of the chief demons under Satan: I prefer from Re 9:1, the former.

bottomless pit--Greek, "abyss."

Abaddon--that is, perdition or destruction (Job 26:6; Pr 27:20). The locusts are supernatural instruments in the hands of Satan to torment, and yet not kill, the ungodly, under this fifth trumpet. Just as in the case of godly Job, Satan was allowed to torment with elephantiasis, but not to touch his life. In Re 9:20, these two woe-trumpets are expressly called "plagues." Andreas of Cæsarea, A.D. 500, held, in his Commentary on Revelation, that the locusts mean evil spirits again permitted to come forth on earth and afflict men with various plagues.