John of Damascus
John of Damascus studied religion. He also studied law, theology, philosophy and music. He is said by some sources to have served as a Chief Administrator to the Muslim caliph of Damascus before he became a priest. He wrote works about Christianity. He composed hymns that are still used by Greek Orthodox churches around the world. He is considered "the last of the Fathers" of the Eastern Orthodox church. He is best known for arguing to let people use pictures of Greek Orthodox saints, which are called "icons". He is also honored by Catholic churches, specifically the Roman Catholic Church.