Today an ancient mystery. Who dunnit? Who could have been so mean that John would refer to him in the Book of Revelations?
The Scripture seems clear:
And that no man might buy or sell, save he that had the mark, or the name of the beast, or the number of his name. Here is wisdom. Let him that hath understanding count the number of the beast: for it is the number of a man; and his number is Six hundred threescore and six. (Rev. 13:17-18)
But is it? The number 666 is thought to refer to Nero according to ancient numerology. But more than 100 years ago other indications were found: here you can see a fragment papyrus 4499 from Oxyrhynchus fragment. It seems clear that the number is χιϛ (616) and not χξς (666).
But if it's not 666 it cannot be Nero. And if it's thought to be 616 it could be Caligula. Too bad for all those RFID critics, Metal bands, George W. critics, etc.