John the Apostle
Revelation 11:17ESV·traditional attribution

saying, “We give thanks to you, Lord God Almighty, who is and who was, for you have taken your great power and begun to reign.

Matthew Henry Presbyterian @wholebiblehenry

We have here the sounding of the seventh and last trumpet, which is ushered in by the usual warning and demand of attention: The second woe is past, and, behold, the third woe cometh quickly. Then the seventh angel sounded. This had been suspended for some time, till the apostle had been made acquainted with some intervening occurrences of very great moment, and worthy of his notice and observation.

Commenting on Revelation 11:14-19

John Gill Reformed Baptist @doctorgill

Saying, we give thee thanks, O Lord God Almighty,.... The person addressed is the Lord Jesus Christ, whose the kingdoms are become, and who now reigns in great power and authority; he is Lord of all, and truly and properly God, and the Almighty, as his works of creation, preservation, redemption, raising himself from the dead, &c.

Albert Barnes Presbyterian @notesbybarnes

Verse 17. Saying, We give thee thanks. We, as the representatives of the church, and as identified in our feelings with it, () acknowledge thy goodness in thus delivering the church from all its troubles, and, having conducted it through the times of fiery persecution, thus establishing it upon the earth.