In Revelation 9:11, is Apollyon Satan or a fallen angel?

On Gog, the answer is both. On Apollyon: the names Abaddon and Apollyon are used only here in the New Testament. Abaddon stands for the Hebrew word found in Job and the Psalms, where it is equated with Sheol, death, or hell. Apollyon appears only in Apocalypse 9:11, with no pedigree in the Old Testament or the Septuagint; both words refer mainly to death and destruction. The Latin Vulgate adds the phrase 'and in Latin his name is Exterminans' at the end of Apocalypse 9:11, but that phrase appears in no Greek manuscript. It is a gloss added by a Latin copyist that was probably a marginal note and made its way into the text, as happened with 1 Corinthians 4:6. The Latin Codex Fuldensis, from 541 to 546 A.D., does not have the phrase, and Codex Sinaiticus and Codex Alexandrinus have an article before 'angel.' The fact that both the Hebrew name Abaddon and the Greek name Apollyon are revealed about this demon means John wants to impart the same truth he gives about Satan in Apocalypse 12:9, the serpent of old called the devil and Satan. Satan was at work in the Old Testament against the Jews, who spoke Hebrew, and he is now at work in the New Testament against the Church, which speaks Greek. So these demons, known to the Jews as Abaddon and to the Greeks as Apollyon, have been operating since the dawn of time and will continue to the end.