Saint Michael the Archangel isn't a saint, but rather he is an angel, and the leader of all angels and of the army of God.
This is what the title "Archangel" means, that he is above all the others in rank.
St. Michael has four main responsibilities or offices, as we know from scripture and Christian tradition.
Very little is known about St Michael other than what we know from scriptures, which themselves are sparse.
Today, St. Michel is invoked for protection, especially from lethal enemies. He is also the patron of soldiers, police and doctors.
Prayer to Saint Michael
Saint Michael the archangel, defend us in battle. Be our protection against the wickedness and snares of the Devil. May God rebuke him, we humbly pray, and do thou, O Prince of the Heavenly hosts, by the power of God, cast into Hell Satan, and all the evil spirits who prowl about the world, seeking the ruin of souls.