Saint John Cassian – John Cassian (c. AD 360 – c. 435), also known as John the Ascetic and John Cassian the Roman (Latin: Ioannes Eremita Cassianus, Ioannus Cassianus, or Ioannes Massiliensis),[2] was a Christian monk and theologian celebrated in both the Western and Eastern churches for his mystical writings. Cassian is noted for his role in bringing the ideas and practices of Christian monasticism to the early medieval West.

John Cassian – Wikipedia

https://en.wikipedia.org/wiki/John_Cassian

John Cassian (c. AD 360 – c. 435), also known as John the Ascetic and John Cassian the Roman (Latin: Ioannes Eremita Cassianus, Ioannus Cassianus, or Ioannes Massiliensis),[2] was a Christian monk and theologian celebrated in both the Western and Eastern churches for his mystical writings. Cassian is noted for his role in bringing the ideas and practices of Christian monasticism to the early medieval West.