David J. Williams thinks that we cannot say "who" or "what" the man of lawlessness is. He writes that the "man" might be "an individual or a group, a government or an institution" (David J. Williams, 1 and 2 Thessalonians, 124). Yet Williams goes on to identify the man of lawlessness with the Beast in Rev. 13 and thinks that the man-beast is the Antichrist.
However, other commentators believe that the man of lawlessness represents a part of the Church: the part that apostatizes from God. Ralph Earle seems to take this stance, though his treatment of the issue is somewhat ambiguous to me. He suggests that the man is linked with apostasy in the Church and lawlessness in the land. He even contends that there was once a time "when the Bob Ingersolls railed and ranted against Christianity." But now "this opposition comes from within the Church" (Ralph Earle, Word Meanings, 375).
It's probably no secret that I would say 2 Thessalonians indicates that the man is a group of persons inside the realm of professed Christianity who apostatize from God; for it's in the Temple of God [the Christian congregation] that the "man" takes his seat (2 Thess. 2:4). He evidently declares himself to be "a god" and he is an apostate, suggesting that the man must be a professed worshiper of God who draws away from the living Deity. But another reason we might contend that the man is not an individual is mentioned in 2 Thess. 2:7, 8.
In these fateful passages, Paul writes that the mystery of lawlessness was already at work in the first century. And yet, the mystery (i.e. the man and his activities) is still present when the Lord Jesus Christ executes his righteous judgment upon this wicked age.
How could one human's life or influence extend from the first century until now? This view seems untenable to me. And if my memory serves me correctly, even Augustine of Hippo (in the City of God) said that the man of lawlessness was composed of those who went out from the Church because they were not, in the final analysis, genuine Christians. While I'm not being dogmatic about the identity of the man of lawlessness, I do believe that 2 Thessalonians is not talking about one man when it mentions this lawless and ungodly figure.