Oecumenius

And he says that "the beast which was, and is not." And it "is the eighth, and is of the seven, and goes to destruction." And he appointed the Devil first and last and a fellow counselor of the seven. For how would this one not also be a ruler who made even the seven utterly wicked?

Commentary on Revelation ↗

Bede

And the beast that was, and is not, even he is the eighth, etc. The Antichrist, who is to rule at the end of the world, because of the unity of the same body of the wicked, of which he is the head, belongs to the number of the kingdoms of the world; but because of the singular power of his wickedness, he is also contained in the order of his own proper place.

Commentary on Revelation ↗

Victorinus of Pettau

"And the beast which thou sawest is of the seven." Since before those kings Nero reigned. "And he is the eighth." He says only when this beast shall come, reckon it the eighth place, since in that is the completion. He added:- "And shall go into perdition." For that ten kings received royal power when he shall move from the east, he says. He shall be sent from the city of Rome with his armies. And Daniel sets forth the ten horns and the ten diadems. …

Commentary on the Apocalypse of the Blessed John ↗