Ya know, Satan himself doesn't know. He's had someone in the wings since Genesis 3:15, Pharaoh, Antiochus, Herod, Stalin, Hitler... As the days grow shorter he'll be allowed to do more and more (2 Thess 2:7) and when he is kicked down to the earth he knows he has but a short time (Rev 12:12). He will be called the Assyrian (Micah 5:5-6) (funny since they no longer exists, but do by another name today as Kurdistan), he will understand "dark sentences" and by this means he will by peace destroy many (Daniel 8:23-25; Rev 6:2 - Islam believe this verse to refer to their messiah called the Mahdi) but in the end Jesus shall destroy him by the words of His mouth (Rev 19:19-20:3), he will make a convent with the Jews for one week (7 years) (Dan 9:27), allow the building of the temple (Rev 11:1-2) and stop the sacrifices after 1150 days. The antichrist will honor war, reject his heritage, and treat women like 2nd class citizens and not listen to their pleas (Dan 11).
How will we know him? It is my belief we won't because we'll be raptured out. But if we are not, then we will see the Two Witness preach for 1260 days, and do many signs and wonders and they will kill anyone that tries to stop them by fire proceeding out of their mouths, then be killed by the antichrist and lie dead for 3.5 days, come back to life and be raptured to heaven, and CNN will run it live. (Rev 11) I believe they will be killed on Passover 3.5 years into this 7 year period and declare himself God and desecrate the Temple spoken of by Jesus (Mat 24:15) and Israel is to flee to Petra for 1260 days and the Lord will return to defeat the antichrist on the Feast of Trumpets, on 1 Tishri, and He will begin His 1000-year reign (Rev 20).
Read up on what
@Cosmicwaffle said because the book Revelation has to very important things no other book has: a warning not to change anything about the book, (Rev 22:19) and it contains gematria (computing the numerical value of words, based on those of their constituent letters) i.e. Rev 13:18. In Greek, what is translated as 666, are the values of each of those letter when added come to 666 (600+60+6). But in the Greek there's no value. Read the verse... then look at all the things in this image:
Revelation 13:18 (KJV)
Here is wisdom. Let him that hath understanding count the number of the beast: for it is the number of a man; and his number [is] Six hundred threescore [and] six.
I used to live in Bahrain (small island nation in the Persian Gulf) and I showed the image of the Greek rotated to Arabic speakers and they said it means "In the name of Allah" which is interesting because that is the call of Islam against all who are not Muslim. What is it Jesus warned us?
John 5:43 (KJV)
I am come in my Father's name, and ye receive me not: if another shall come in his own name, him ye will receive.
I believe John warned those who would copy his work not to make any changes. Having written what he saw (Rev 1:11; 1:19) I believe he wrote
Bismillah and I have a whole section dedicated to it in my study (
http://www.abdicate.net/book.aspx) in appendix L. Not understanding the drawing that John made, it could be that they thought he wrote those Greek letters. Amazing how even then God had a language prepared for His word!
Just my 2 cents and I hope it helps.