Unlike most saints, Michael is not a human being at all. He is a senior angel (usually called an archangel) described in the book of Daniel as a prince. He is also mentioned in the Revelation to John.
Both references are military in context, suggesting that St.
Michael is the commander of the heavenly army. In Revelation it is St.
Michaels angels who defeat the dragons and drive Satan out of heaven.
He is usually depicted standing over the dragon with a spear, and our East window is no exception where St.
Michael stands in the central panel between Christ at the top and the Devil at the bottom.