Five books of the New Testament are ascribed to authors named John: the fourth Gospel, three short epistles, and Revelation. There is considerable debate about how many Johns were involved – and whether any of them was the apostle of that name.
According to Wikipedia, the three epistles were all probably written by the same author; and indeed tradition attributes the gospel and the three epistles to a single author, although most modern scholars agree that it was not John the apostle.
Wikipedia speaks of John the Presbyter, "an obscure figure of the early Church", who may or may not be the Apostle John. He may be the author of the gospel, the epistles, and/or the Revelation.
A more likely candidate for authorship of Revelation, however, seems to be John of Patmos, who lived in the first century AD and is considered to have been exiled to the Greek island of that name following anti–Christian persecution under the Roman emperor Domitian.
© Haydn Thompson 2020