'Mighty Angel' in the Bible

And I saw a mighty angel proclaiming in a loud voice, "Who deserves to break the seals on it and open the book?" [Note: This "book" was probably a rolled up scroll written on both sides, with wax seals keeping it from unrolling and its contents from being exposed].

And I saw another mighty angel coming down from heaven. He was covered by a cloud and there was a rainbow above his head. His face was like the sun and his legs were like pillars of fire.

Then a mighty angel picked up a rock the size of a huge millstone and threw it into the ocean, saying, "This is how the great city of Babylon will be violently thrown down and will never be found again.