Michael is the name of the archangel who confronts Satan and his angels as they try to attack God upon His throne in the book The Indwelling. He later appears in the book Desecration to offer divine help for Operation Eagle; in the Dramatic Audio Series, his sudden appearance frightens George Sebastian in the process, for which he apologizes. In Glorious Appearing, he is responsible for chaining up Satan and sealing him in the bottomless pit for a thousand years.
At the end of the Millennial Kingdom, he is also present for Nicolae's and Leon's judgements.
Michael's formal title is General of the Host of Heaven. As an archangel, he is presumably more resistant to sonic and electromagnetic weapons than other Angels.