Most people are aware of the archangel Michael, although he is mentioned only a few times in the Bible. Michael's most remarkable role in the Bible is surely the battle with the dragon in the Book of Revelation, 12: "And there was war in heaven: Michael and his angels going forth to war with the dragon; and the dragon warred and his angels; And they prevailed not, neither was their place found any more in heaven. And the great dragon was cast down, the old serpent, he that is called the Devil and Satan, the deceiver of the whole world; he was cast down to the earth, and his angels were cast down with him."
Beyond the Bible, however, the archangel Michael has been memorialized in many cult practices and legends dating back to late antiquity. Michael appears in several apocryphal books of early Christianity, for example, assisting Christ in the harrowing of hell. Here is a passage from the Gospel of Nicodemus that describes the rescue of Adam and the saints from hell: "But the Lord holding the hand of Adam delivered him unto Michael the archangel, and all the saints followed Michael the archangel, and he brought them all into the glory and beauty of paradise."
In the Conflict of Adam and Eve with Satan, Michael helps God give the gift of light to Adam after his expulsion from Eden: "And God considered Adam's thought, and sent the angel Michael as far as the sea that reaches India, to take from there golden rods and bring them to Adam. This did God in His wisdom in order that these golden rods, being with Adam in the cave, should shine forth with light in the night around him, and put an end to his fear of the darkness."
There are also important legends about Michael in both the Jewish and Islamic traditions. Jehovah's Witnesses believe the Jesus and Michael are the same being. Mormons identity Michael with Adam.
One of the major feasts of Saint Michael the Archangel is September 29, a holiday known as Michaelmas (also part of the British school calendar tradition, as at Oxford).
May 8 is also a holiday for the archangel Michael, commemorating the "Apparition of Saint Michael," which took place at Mount Gargano in Italy in the year 490. You can read an account of this apparition in the Breviary for this day; look under the second nocturn, fifth lesson.
In this image of Saint Michael, you can see the Latin motto, quis ut deus, "who is as God (El)?" which is the meaning of Michael's Hebrew name: