St. Michael, or Archangel Michael is mentioned three times in the Book of Daniel.
The idea that Michael was the advocate of the Jews became so prevalent that, in spite of the rabbinical prohibition against appealing to angels as intermediaries between God and his people, Michael came to occupy a certain place in the Jewish liturgy.
In the New Testament Book of Revelation, Michael leads his angels against the dragon ("the Devil and Satan") and his angels during the war in heaven where he defeats the dragon. In the Epistle of Jude, Michael is specifically referred to as "the archangel Michael".
Sanctuaries to Michael were built by Christians in the 4th century, when he was first seen as a healing angel. Over time his role became one of a protector and the leader of the heavenly host against the forces of evil.