666 is the sum of the numbers in the name Nero. Also, Nero was brutal to the Christians as well, he beheaded Paul and crucified Peter, as well as tormented many other Christians.

His name is the Greek numerical equal 666, he was written about by John in the book of revelations as the beast sent by the Devil as the enemy of all christians in code (666) as to name him in person would mean death to any church person.

In Hebrew gematria, every letter has a corresponding number. Summing these numbers gives a numeric value to a word or name. The Greek spelling, “Neron Caesar,” transliterates into Hebrew as “נרון קסר” or “nrwn qsr”. Adding the corresponding values yields 666, as shown: Resh = 200 Samekh = 60 Qoph = 100 Nun = 50 vav = 6 Resh = 200 Nun = 50 TOTAL = 666 By contrast, the Latin title for Nero is spelled simply “Nero Caesar,” which transliterates to “נרו קסר” or “nrw qsr” and has a value of 616, which explains that variation in Papyrus 115 (a mid 3rd Century [fragmentary] manuscript of the NT, that includes the Revelation) The hypothesis that 666 or 616 is a code for a Roman emperor does have historical support. The emperors were noted for their oppression of both Jews and Christians. Both communities were known to use numerology, codes and symbols (such as the Ichthys) when living under Roman rule to avoid persecution. Regarding Nero being called "the devil's son", I've never heard or read any Christians today calling Nero that specifically, though many modern Dispensationalists (who DON'T think Nero is the Beast, but rather that the Beast is someone to come after the Church is Raptured, during the Great Tribulation) may call the Beast the Devil's son -- and more than a few may mean it literally, judging by such nonsense as the Left Behind series. However, in ancient Semitic usage, the expression "son of _______" typically meant that the person so described exhibited the character of whatever was in the blank - hence such expressions as "son of a camel" and "son of a dog" and "son of Hell" and also "son of God": the expression was a reference to the person's character and behavior, not his actual parentage. In that regard, Nero certainly could well be described as "son of Satan" as he was the enemy and would-be destroyer of both Israel and the Church, and the enemy and would-be supplanter of God.