One Gospel, three letters, and the book of Revelation are all attributed to “John.” We read about several Johns in the New Testament, including John the Baptist and John the apostle, the son of Zebedee. Note that each of them required some additional designation to distinguish them from others with the same name. So how did those who attributed the Gospel, letters, and Revelation to “John” expect readers to know which John they meant?
Of the New Testament works, only Revelation names its author explicitly as “John.” Revelation is written in much poorer Greek than the Gospel and letters are, and it even spells the name Jerusalem in Greek differently than the Gospel does. So it is extremely unlikely that the same person wrote all of these books. Some scholars therefore refer to the author of Revelation as “John the seer” or “John of Patmos” to distinguish him from the purported author of the Gospel and letters. Given that apocalyptic works were typically written pseudonymously in the names of earlier authorities, as though those individuals had predicted current and future events, the possibility must also be considered that Revelation was written by someone pretending to be John the apostle predicting the events of Nero’s time and thereafter.
The Gospel and letters do not name their author, or authors. The titles affixed to these books in modern Bibles (for example, the “Gospel according to John”) first appear in manuscripts a century or more after these works are thought to have been written.
The Gospel and letters may or may not be by the same author (and in the case of the Gospel, the “author” could be someone more like a final editor working with various source materials). But the shared style and terminology indicates that if these books are not by the same author, then they must be by authors who were part of a community that shared certain traditions and emphases.
Within the Gospel itself, an individual referred to as the “disciple whom Jesus loved” is credited as an author of at least some of the Gospel’s content (John 21:24) by whoever penned the final chapter (apparently someone other than this beloved disciple). The “disciple whom Jesus loved” is not explicitly named within the pages of the Gospel but has almost universally been identified as John the son of Zebedee (one of Jesus’ twelve apostles) throughout the history of the church. However, J. Kreyenbühl and others since have pointed out that John 11:3 refers to Lazarus as someone whom Jesus loved, and so perhaps Lazarus could be the beloved disciple and source behind the Gospel.
A second-century church leader named Papias is often cited as an important early source of information regarding the church’s traditions of authorship. Unfortunately Papias’s works have not survived, so we hear from him indirectly, in quotations of others. According to Eusebius, Papias mentioned his efforts to find out what a variety of key figures, including John the apostle, said (using the past tense), and also what Aristion and John the Elder say (using the present tense). On that basis, it has been suggested (by Hengel and others) that this “John the elder” may have written the Gospel of John and the letters of John (note how the author refers to himself in 2John 1 and 3John 1). If this were the case, then the tradition that these works were written by someone named John would be correct, even if that person was not John the apostle.