John the Apostle
Revelation 8:8BSB·traditional attribution

Then the second angel sounded his trumpet, and something like a great mountain burning with fire was thrown into the sea. A third of the sea turned to blood,

Matthew Henry Presbyterian @wholebiblehenry

Observe, I. The first angel sounded the first trumpet, and the events which followed were very dismal: There followed hail and fire mingled with blood, etc., Rev 8:7. There was a terrible storm; but whether it is to be understood of a storm of heresies, a mixture of monstrous errors falling on the church (for in that age Arianism prevailed), or a storm or tempest...

Commenting on Revelation 8:7-13

John Gill Reformed Baptist @doctorgill

And the second angel sounded,.... His trumpet: and as it were a great mountain burning with fire was cast into the sea; by which is meant not the devil, as some think; called a "mountain" from his height of pride, a great one from his might and power, and a "burning" one from his great wrath and malice against Christ, his Gospel, and his people...

Albert Barnes Presbyterian @notesbybarnes

Verse 8. And the second angel sounded. Compare . This, according to the interpretation proposed above, refers to the second of the four great events which contributed to the downfall of the Roman empire. It will be proper in this case, as in the former, to inquire into the literal meaning of the symbol, and then whether there was any event that corresponded with it.