John the Apostle (Aramaic: ywHnn shlyH' Yohanan Shliha; Hebrew: yvkhnn bn zbdy Yohanan ben Zavdi; Koine Greek: Ioannes; Coptic:  or ; Latin: Ioannes; c. AD 6-100) was one of the Twelve Apostles of Jesus according to the New Testament, which refers to him as Ioannes. Generally listed as the youngest apostle, he was the son of Zebedee and Salome or Joanna.

The author of the Book of Revelation identifies himself as "Ioannes" ("John" in standard English translation) The early 2nd century writer, Justin Martyr, was the first to equate the author of Revelation with John the Apostle. Most biblical scholars now agree that these were not separate individuals and that John the apostle wrote the Book of Revelation.  John the Presbyter, an obscure figure in the early church, has also been identified with the seer of the Book of Revelation by such authors as Eusebius in his Church History (Book III, 39)  and Jerome.  John is considered to have been exiled to Patmos, during the persecutions under Emperor Domitian. Revelation 1:9 says that the author wrote the book on Patmos: "I, John, both your brother and companion in tribulation... was on the island that is called Patmos for the word of God and for the testimony of Jesus Christ." Adela Yarbro Collins, a biblical scholar at Yale Divinity School, writes:  Early tradition says that John was banished to Patmos by the Roman authorities. This tradition is credible because banishment was a common punishment used during the Imperial period for a number of offenses. Among such offenses were the practices of magic and astrology. Prophecy was viewed by the Romans as belonging to the same category, whether Pagan, Jewish, or Christian. Prophecy with political implications, like that expressed by John in the book of Revelation, would have been perceived as a threat to Roman political power and order. Three of the islands in the Sporades were places where political offenders were banished. (Pliny Natural History 4.69-70; Tacitus Annals 4.30)  Some modern higher critical scholars have raised the possibility that John the Apostle, John the Evangelist, and John of Patmos were three separate individuals. These scholars assert that John of Patmos wrote Revelation but neither the Gospel of John nor the Epistles of John. For one, the author of Revelation identifies himself as "John" several times, but the author of the Gospel of John never identifies himself directly. Some Catholic scholars state that "vocabulary, grammar, and style make it doubtful that the book could have been put into its present form by the same person(s) responsible for the fourth gospel."

What was in the book of revelation?