And he causes all, the small and the great, and the rich and the poor, and the free men and the slaves, that they be given a mark on their right hand or on their forehead,  and that no one will be able to buy or to sell, except the one who has the mark, either the name of the beast or the number of his name.  Here is wisdom. Let him who has understanding calculate the number of the beast, for it is the number of man; and his number is 666.
Revelation 13:16-18