Now war arose in heaven, Michael and his angels fighting against the dragon; and the dragon
and his angels fought, but they were defeated and there was no longer any place for them
in heaven. And the great dragon was thrown down, that ancient serpent, who is called the Devil
and Satan, the deceiver of the whole world -- he was thrown down to the earth, and his angels were
thrown down with him. -- Revelation 12:7-9 (Revised Standard Version)

Who is Saint Michael?

The symbol of Archangel St. Michael is the balance scales, as tradition has it that he will weigh human souls on the Day of Judgment.

Michael is the only angel to have a feast day in the Lutheran calendar and the only angel to have a feast day on any calendar prior to the 9th century. He is commemorated on Sept 29, the feast of St. Michael and All Angels on the Lutheran calendar. Churches have been dedicated to St. Michael since the fourth century; the first being near Constantinople.

Michael is mentioned by name several times in Holy Scripture: the passage from Revelation above, twice in Daniel (10:13 and 12:1), and also in Jude 9. He is also believed to have been the mysterious warrior encountered by Joshua who introduces himself as Commander of the Lord's army (Joshua 5:13-15).

Although traditionally credited with driving Lucifer and his legions from heaven, St. Michael was first venerated as a healer, not a warrior, in Phrygia. Pope Gregory the Great credited St. Michael with ending the plague in Italy when he saw Michael sheathing a flaming sword.

Michael comes from the Hebrew "Mikha'el" (Who is like God?), which is said to be the war cry of the angels of God before going into battle. Michael is believed by many to be the highest ranking of all the angels. He is the protector of God's chosen people, and thus he is also the protector of the Church and her members against the evil one. He is the protector of Christian armies.

Resource: Catholic Encyclopedia - St. Michael the Archangel: http://www.newadvent.org/cathen/10275b.htm