This calls for wisdom. Let the person who has insight calculate the Number of the Beast, for it is the Number of a Man. That number is 666.
– Revelation 13:18
A true riddle is found in Revelation 13:18, where the number 666 is apparently an obscure reference to some individual. The attempts to interpret it are legion and no consensus reigns…Great caution needs to be exercised in interpreting the “dark sayings” of the Scripture. Special care should be given to understand exactly what the words in the original language meant. Due regard to context, always important, is esp. so in such instances.
– Encyclopedia of The Bible, BibleGateway.com