Philotheus Boehner was born as Heinrich Boehner on February 17, 1901, in Lichtenau, Westphalia. He joined the Franciscan Order in 1920, and was given the new name "Philotheus", which is the Latin form of the Greek "Philotheos", and means "friend of God". In 1927 he became a priest, but he was very ill with tuberculosis and not expected to live much longer. While resting to try and get better from being sick, he started to translate Étienne Gilson's work on Saint Bonaventura. In the 1930s, he and Gilson became close friends.