St. John the Evangelist on Patmos by Hieronymous Bosch, circa 1489. [Image from the Wikipedia 'John of Patmos' page, public domain, via Wikimedia Commons.]
John of Patmos is the name given to the author of the book of Revelation (or book of the Apocalypse) in the New Testament. According to the text of Revelation, the author, who gives his name as 'John,' is living on the Greek island of Patmos. Many believe John was in exile. In Revelation, he writes to the seven Christian churches in Asia to relate two apocalyptic visions he has had. John of Patmos is often referred to as John the Divine, or John the Theologian, and the message he received is considered divine Revelation by most Christians. Apocalypse is a Greek word for revelation or uncovering, and divine an old Anglican usage meaning theologian. He is also known as the Eagle of Patmos and John the Seer. Several Christian denominations regard him as a prophet and a saint.
John of Patmos is traditionally believed to be the same person as both John, the apostle of Jesus and John the Evangelist, author of the Gospel of John. Justin Martyr, writing in the early 2nd century, was the first to equate the author of Revelation with John the apostle. Some biblical scholars now contend that these were separate individuals.[a]
a. Wikipedia, 'John of Patmos'. Web, n.d. URL = https://en.wikipedia.org/wiki/John_of_patmos.