Arthur, legendary king of the Britons, was called the “once and future king”. The Welsh called Arthur Pendragon — the “head dragon” — Mab Darogan, the “son of prophecy”, one who would return someday to lead his people back to glory.
Perhaps not coincidentally, the Bible’s prophecy of a future world leader describes him as a servant of the “great dragon”, a king who “has not yet come” — a future king who was also one of the seven represented by a seven-headed beast, six of whom had lived at the time of John the Revelator or earlier and one who would come for “only a little while”.
In short, the Antichrist would be a once and future king.
King Arthur in a different light: Once and Future Thing, a tale for Halloween future, now online at Writer’s Cramp.