Nero was the Beast of Revelation. “The Beast” was his nickname back then because of his reputation for cruelty.
But more interesting is the fact that 666 (the number of the beast) is a popular form of encrypting someone’s name in that time period in Rome. Each letter of the Greek alphabet was assigned a number. You add up all the numbers for each letter and the result can be used to verify a name. It’s impossible to reliably reverse this cypher so it is a good way of keeping the actual name secret. They have unearthed ruins from ancient Roman cities where people have written graffiti “I love 483” and such.
Nero’s name was Neron Ceasar and it is encrypted “666” in Greek. Hebrew had a similar from of popular encryption. Nero’s name was Neron Kaiser in Hebrew and the Hebrew New Testament says the number of the beast is 616.
Oh, did Nero cause everyone to have a mark on their hand or forehead? Must have missed that.