It is as you stated; the mark of that one is 666, and I do agree in Rev it does appoint to an individual not mankind as a whole. However, I do also find it interesting how in 1 Kings 10:14 and 2nd Chronicles 9:13 it reads that Solomon received 666 talents of gold each year (*in addition to what he received from merchants, traders, various kings etc). My interpretation of this depicting the full representation of the sin that had corrupted man. Solomon would have been everything a worldly man would strive for and yet in the end as he states it was all "striving after the wind, vanity upon vanity". God gives us Solomon as an example that mankind to prove nothing can satisfy us outside of Him, as that is our purpose, to glorify God and worship Him forever. I just those particular verses stand out to me (among others) as Paul says ultimately we will either be a slave to righteousness or a slave to sin.