2 Thessalonians 2:3-10

(3) Let no one deceive you by any means; for that Day will not come unless the falling away comes first, and the man of sin is revealed, the son of perdition, (4) who opposes and exalts himself above all that is called God or that is worshiped, so that he sits as God in the temple of God, showing himself that he is God. (5) Do you not remember that when I was still with you I told you these things? (6) And now you know what is restraining, that he may be revealed in his own time. (7) 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. (8) And then the lawless one will be revealed, whom the Lord will consume with the breath of His mouth and destroy with the brightness of His coming. (9) The coming of the lawless one is according to the working of Satan, with all power, signs, and lying wonders, (10) and with all unrighteous deception among those who perish, because they did not receive the love of the truth, that they might be saved.

  Daniel 7:8

(8) I was considering the horns, and there was another horn, a little one, coming up among them, before whom three of the first horns were plucked out by the roots. And there, in this horn, were eyes like the eyes of a man, and a mouth speaking pompous words.

  Daniel 7:21

(21) "I was watching; and the same horn was making war against the saints, and prevailing against them,

  Daniel 7:25

(25) He shall speak pompous words against the Most High,
Shall persecute the saints of the Most High,
And shall intend to change times and law.
Then the saints shall be given into his hand
For a time and times and half a time.

  Revelation 13:11-18

(11) Then I saw another beast coming up out of the earth, and he had two horns like a lamb and spoke like a dragon. (12) And he exercises all the authority of the first beast in his presence, and causes the earth and those who dwell in it to worship the first beast, whose deadly wound was healed. (13) He performs great signs, so that he even makes fire come down from heaven on the earth in the sight of men. (14) And he deceives those who dwell on the earth by those signs which he was granted to do in the sight of the beast, telling those who dwell on the earth to make an image to the beast who was wounded by the sword and lived. (15) He was granted power to give breath to the image of the beast, that the image of the beast should both speak and cause as many as would not worship the image of the beast to be killed. (16) He causes all, both small and great, rich and poor, free and slave, to receive a mark on their right hand or on their foreheads, (17) and that no one may buy or sell except one who has the mark or the name of the beast, or the number of his name. (18) 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 19:20

(20) Then the beast was captured, and with him the false prophet who worked signs in his presence, by which he deceived those who received the mark of the beast and those who worshiped his image. These two were cast alive into the lake of fire burning with brimstone.
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Paul wrote II Thessalonians to correct their false impression by telling them what Christ had revealed to him regarding the "gathering together with Christ" of those dead in Christ and those remaining alive when He returned. He opens by telling them, first of all, that Christ's return will be preceded by a period of apostasy that could include anything from a falling away, a departure from doctrine or teaching, all the way to and including an outright political rebellion.
The second sign would be the appearance of the man of sin. This person has four different names or titles, but all of them are described similarly: the man of sin (II Thessalonians 2:3-10), the little horn (Daniel 7:8), the two-horned lamb who spoke like a dragon (Revelation 13:11-18), and the false prophet (Revelation 19:20). The description in each location is not exactly alike, but each adds to what the other gives. Consider this summary of comparisons.

In each case, the person described appears at the time of the end. This is the one piece of information that every one of them has in common.
In three of the four, his end—his destruction or annihilation—comes at the return of Jesus Christ (Daniel 7:8-9; II Thessalonians 2:3; Revelation 19:20).
In three of the four, it directly states or strongly implies the person speaks with great pompous words (Daniel 7:8-9; II Thessalonians 2:4; Revelation 13:11-14).
In three of the four, it directly states the person does miraculous, supernatural signs (II Thessalonians 2:9; Revelation 13:13-15; Revelation 19:20).
In two of them, the signs are done in the presence of the Beast, showing they are not the same figure (Revelation 13:13-15; 19:20).
In two of them, he deceives and leads people into idolatry (II Thessalonians 2:4,9-10; Revelation 13:12,14).
In two of them, he either makes war against the saints or causes those who would not worship the beast to be put to death (Daniel 7:21; Revelation 13:15).
In two of them, he either thinks to change times and law—suggesting the law of God—or he sets himself in the Temple of God, proclaiming himself to be God. The implication is that he has the authority to do these things (Daniel 7:25; II Thessalonians 2:4).
In two of them, his period of greatest influence is three and a half years (Daniel 7:25; Revelation 13:5).

All of these scriptures are describing the same person. The Bible shows that this person—the man of sin—has a direct connection to a large political power and has a religious influence. It should be understood that we are dealing with a personage and with prophecies of global significance.

— John W. Ritenbaugh