Michael is the greatest of the Archangels of Heaven equaled only by Lucifer. It was Michael who on God's Command threw Lucifer into Hell. His true Vessel is Dean. Castiel describes him as far more powerful than Raphael, which would make him tremendously powerful.
Michael was first mentioned in 2.13 Houses of the Holy, when Sam notices a painting of Micahel killing Lucifer by the Renaissance painter Raphael in the church.
Father Reynolds: That's right. The archangel Michael, with the flaming sword. The fighter of demons, holy force against evil.Father Reynolds: Well, I like to think of them as more loving than wrathful; but yes, a lot of Scripture paints angels as God's warriors. "An angel of the Lord appeared to them, the glory of the Lord shone down upon them, and they were terrified." Luke. Two nine.
Sam: So they're not really the Hallmark card version that everybody thinks? They're fierce, right? Vigilant?
Michael in lore
Michael is an archangel in Jewish, Christian and Islamic tradition. He is most known as a leader of the armies of God against Lucifer.