For the mystery of iniquity doth already work: only he who now letteth will let, until he be taken out of the way.
who do you think the HE is ?
The restrainer.
The one who is restraining the false christ, so that he will be revealed in his own time.
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. 2 Thessalonians 2:5-8
We know that He who is restraining the false christ, does so according to God's will, whether it is an angel or the Holy Spirit, this restraining of the false christ is done so that
he will be revealed in
his own time, and this revealing will continue until the coming of the Lord, whereby the false christ will be destroyed by the brightness of His coming.
So, ultimately the One restraining is God the Father, who orchestrates this work of restraining according to the counsel of His will, through the agency of the Holy Spirit, and then ultimately through the angels who influence a multitude of events on a global scale so that this false christ will rise to power at just the exact time God the Father intends.
JLB