Revelation 13 The Beasts From the Sea and Earth
Well, this was a "beastly" study! We met "The" Antichrist. (I say "The" because, as john mentions in his epistles, "... there are already many anti-christs in the world already." John's epistles are the ONLY place the word "antichrist" is used in the bible. He is referred to by 43 other titles in other scripture, from "Man of Lawlessness" to "Beast from the Sea." But "Antichrist" is what we have commonly come to call him.
Then we met the "Beast from the earth" -- more commonly known as "The False Prophet" who deceives the whole world (except those whose names are written in the Lamb's Book of Life) and forces them to take the Mark of the Beast. He is the "Lamb that spoke like a Dragon" -- the unholy spirit. While the Holy Spirit on says what God tells him to say (He IS the spirit of Jesus) the False Prophet will speak what SATAN tells him to say.
So now, with the Dragon (Satan) from chapter 12 who, in 13:1 "And the dragon stood on the sand of the seashore." as he indwells the Beast from the Sea (Antichirst) joined the Beast from the Earth (False Prophet) and we have the whole UNHOLY Trinity.
So that is my theory (out many out there) on what 666 means - one "6" for each of the un-holy trinity. But just in case you want to play with the numerology, there are slides I didn't show with Greek and Hebrew numerology in the PDF file. See how many names you can make add up to 666. : )
Part 1 Video