John the Apostle (יוחנן "The LORD is merciful", Standard Hebrew Yoḥanan, Tiberian Hebrew Yôḥānān) was one of the twelve apostles of Jesus. Christian tradition proclaims he is the same John which wrote the Gospel of John (known as John the Theologian and John the Evangelist) and that which wrote the Book of Revelation (formally called Apocalypse of St. John the Divine) (John the Divine).

According to the New Testament account, John the Apostle was the son of Zebedee, and the brother of James. One tradition gives his mother's name as Salome. They originally were fishermen and fished with their father in the Lake of Genesareth. He was first a disciple of John the Baptist, and later one of the twelve disciples of Jesus. He is revered as a saint by all branches of Christianity that revere saints. The Roman Catholic Church commemorates him on December 27. The Eastern Orthodox Church commemorates him on September 26, and also remembers him on May 8, on which date Christians used to draw forth from his grave fine ashes which were believed to be effective for healing the sick.

John was traditionally held to be the author of five books of the New Testament, including the Gospel of John. However, almost all critical scholars place the writing of the final edition of John at some time in the late first or early second century. See Authorship of the Johannine works.

Catholic/Orthodox tradition says that he and the Virgin Mary moved to Ephesus, where both eventually died. Many Evangelical and other scholars question this, especially due to the advanced age which Mary would have reached by this time. Some believe, however, that there is support for the idea that John did go to Ephesus and from there wrote the three epistles sometimes attributed to him. John was allegedly banished to the Greek island of Patmos, where some believe that he wrote the Book of Revelation.

When St. John was old he trained St. Polycarp, later Bishop of Smyrna. This was important because Polycarp was able to carry John's message to another age.

For more information on the author of the Gospel, see John the Evangelist.