The De Occulta Philosophia (Three Books of Occult Philosophy) is a study of the power of magic and how it relates to religion. It was written by Heinrich Cornelius Agrippa, a German magician, theologian, alchemist and astrologer. John Dee often mentions Agrippa’s book in his own writing. Agrippa appears as a character on a chocolate frog card in the Harry Potter series.
Ramon Lull was a 13th century Majorcan writer and philosopher. He attempted to show that Christian doctrines could be reached through logic from a fixed set of ideas. He also wrote on astrology and was interested in mysticism, for which he was condemned by the Pope.