Who is Apollyon?

During my devotional reading, I am reading through the trumpet judgments. Today’s reading involved the fifth trumpet (Rev. 9:1-11) during which horrible locust like tormenters are released against those who refuse to repent. They are released from the bottomless pit by their ruler, an angel named Apollyon (9:11). Who is this angel?

There is considerable difference of opinion among expositors over the identity of this personage. Some will argue that he is an otherwise unknown fallen angel under Satan (Seiss, Newell, R. L. Thomas, LaHaye). Others argue that he must be Satan himself (J. B. Smith, Scott, Ironside, Ottman, Strauss, Walvoord).

Stewart Custer, From Patmos to Paradise, (Greenville: BJU Press, 2004), 108.

From my initial reading, I thought it could either be one of God’s angels (since God used angels for the destruction of Sodom and Egypt) or one of the fallen angels who serve Satan. But the idea of it being Satan didn’t seem to fit as he is easily identified elsewhere in the book. Whatever the case may be, this is probably where some get the idea that Satan is the ruler of Hell.