What is the Antichrist:

The Antichrist, often called the Beast, is a ruler of the final world empire. This figure declares himself God and persecutes any Christian who refuses to acknowledge his divine title. The Antichrist will declare war on Israel which will last for 31/2 years. According to Revelation, the number “666″ is associated with the Antichrist. However, early copies of Revelation reveal the number 616 instead of 666. The Bible teaches that those who follow the Antichrist will receive a mark on their right hand and forehead.

Scripture Reference:

“Then after the sixty-two weeks the Messiah will be cut off and have nothing, and the people of the prince who is to come will destroy the city and the sanctuary And its end will come with a flood; even to the end there will be war; desolations are determined. And he will make a firm covenant with the many for one week, but in the middle of the week he will put a stop to sacrifice and grain offering; and on the wing of abominations will come one who makes desolate, even until a complete destruction, one that is decreed, is poured out on the one who makes desolate.”

Daniel 9:26-27

Let no one in any way deceive you, for it will not come unless the apostasy comes first, and the man of lawlessness is revealed, the son of destruction, who opposes and exalts himself above every so-called god or object of worship, so that he takes his seat in the temple of God, displaying himself as being God. Do you not remember that while I was still with you, I was telling you these things? And you know what restrains him now, so that in his time he will be revealed. For the mystery of lawlessness is already at work; only he who now restrains will do so until he is taken out of the way. Then that lawless one will be revealed whom the Lord will slay with the breath of His mouth and bring to an end by the appearance of His coming; that is, the one whose coming is in accord with the activity of Satan, with all power and signs and false wonders, and with all the deception of wickedness for those who perish, because they did not receive the love of the truth so as to be saved.

2 Thessalonians 2:3-10