The restrainer (2 Thessalonians 2:6&7) is a bit of an enigma, but has been variously interpreted as the Holy Spirit, the Church, human government, or the archangel Michael.
But to let Scripture speak for itself, here is an except from 2 Thessalonians 2:
1 Now concerning the coming of our Lord Jesus Christ and our being gathered together to Him, we ask you, brothers, 2 not to be easily disconcerted or alarmed by any spirit or message or letter seeming to be from us, alleging that the Day of the Lord has already come. 3 Let no one deceive you in any way, for it will not come until the rebellion occurs and the man of lawlessness—the son of destruction—is revealed. 4 He will oppose and exalt himself above every so-called god or object of worship. So he will seat himself in the temple of God, proclaiming himself to be God.
5 Do you not remember that I told you these things while I was still with you? 6 And you know what is now restraining him, so that he may be revealed at the proper time. 7 For the mystery of lawlessness is already at work, but the one who now restrains it will continue until he is taken out of the way. 8 And then the lawless one will be revealed, whom the Lord Jesus will slay with the breath of His mouth and annihilate by the majesty of His arrival.
9 The coming of the lawless one will be accompanied by the working of Satan, with every kind of power, sign, and false wonder, 10 and with every wicked deception directed against those who are perishing, because they refused the love of the truth that would have saved them. 11 For this reason God will send them a powerful delusion so that they believe the lie, 12 in order that judgment may come upon all who have disbelieved the truth and delighted in wickedness.
