Was St. Michael a real person?

No, he was (is) an archangel in both Christian and Islamic traditions. He is viewed as the "field commander" of the Army of God. He is mentioned by name in the Book of Daniel and the Book of Revelation.Yes, before there was even light and darkness our loving and merciful God had created an army. Why the creator of the universe needed an army to fight against angels that he created is one of the many mysteries of The Bible.