The Apostle Paul
2 Thessalonians 2:4ESV·traditional attribution

who opposes and exalts himself against every so-called god or object of worship, so that he takes his seat in the temple of God, proclaiming himself to be God.

John Calvin Reformed @genevareformer

4 An adversary, and that exalteth himself. The two epithets — man of sin, and son of perdition — intimate, in the first place, how dreadful the confusion would be, that the unseemliness of it might not discourage weak minds; and farther, they tend to stir up the pious to a feeling of detestation, lest they should degenerate along with others.

Matthew Henry Presbyterian @wholebiblehenry

In these words the apostle confutes the error against which he had cautioned them, and gives the reasons why they should not expect the coming of Christ as just at hand. There were several events previous to the second coming of Christ; in particular, he tells them there would be, I. A general apostasy, there would come a falling away first, Th2 2:3.

Commenting on 2 Thessalonians 2:3-12

John Gill Reformed Baptist @doctorgill

Who opposeth,.... Or is an opposer, an adversary of Christ, the antichrist; who opposes him in his kingly office, styling himself the head and spouse of the church, assuming to himself all power in heaven and in earth, taking upon him to dispense with the laws of Christ, and to make new ones; who opposes him in his priestly office, by pretending to offer him...