The Book of Revelation, the last book of the Bible, refers to a tyrannical seven-headed beast that rises from the sea demanding to be worshipped, and poses an associated riddle: “He who has understanding, let him calculate the number of the beast, for it is the number of a man. His number is 666.” All we know about the author of Revelation is that his name is John, which some have assumed to be the apostle John, who wrote the Fourth Gospel. But the writing style of the two books is quite different, and the John of Revelation makes no claim to be an apostle, or even to have known Jesus.
The number of the beast is given as 616 in some early manuscripts, including New Testament papyrus 115, dating from the late 3rd or early 4th century. It may be that 616 was originally introduced as a copying error and subsequently disseminated, but the current view of Biblical scholars favours the number 666.
Eschatology or polemic
Historically, many Christians have believed the Book of Revelation to be a prophecy about the end of the world, but most modern Biblical scholars now consider it to be a polemic against the Roman empire, warning early Christians not to compromise with the Romans.
The 1976 film The Omen popularised the idea that the number 666 would be a birthmark somewhere on the Antichrist, and established the notion that he would be the son of Satan, sent to wrest control of the world from Christ.