"Here is wisdom.
Let him who has understanding calculate the number of the beast, for it is the number of a man: his number is 666"
Revelation 13:18

This indicates that the Mark of the Beast, which will be used as a totalitarian control device to enforce the worship of the man of sin, will be connected with the name of the Antichrist.

The numerical value of his name in the Greek or Hebrew language will be connected with 666.