A considerable amount of historical information supports the position that John is the author of the fourth gospel. Taken together, these data provide a solid claim of Johannine authorship. Many early editions of the Bible list John as the author of the fourth gospel, although no manuscript exists that specifically ascribes authorship to him. For that matter, none of the other gospels specifically name their authors, but the church accepted Matthew, Mark, and Luke as the authors of these gospels very early.
Numerous historical and external evidence support John as the author of the gospel. The earliest known individual to accept Johannine authorship is Theophilus of Antioch (181 CE). Even before this declaration, Tatian, a student of Justin, and Apollinaris, bishop of Hierapolis, recognized John as the author. An indirect affirmation of John’s authorship is by Valentius, author of The Gospel of Truth (140-150 CE), a Gnostic writing in which he cites or references the gospel. He was a second-century heretic who was a resident of Rome and a prolific writer and orator. Examples of other early Gnostic writings referencing material from John's gospel include the Gospel of Philip and the Gospel of Thomas. These writings help define the time of writing of the fourth gospel to a period before the end of the first century CE.
Clement (150-215 CE), head of the Catechetical School in Alexandria (190 CE), wrote that John became a resident of Ephesus after leaving Patmos following the death of Emperor Domitian (ruled from 81 to 96 CE). Polycarp, bishop of Ephesus, sent a letter around 190 CE in which he mentions the burial place of John being in Ephesus. Polycarp became a martyr in 156 CE at the age of 86, which makes his testimony more pertinent. Papias (60-140 CE), bishop of Hierpolis, also supports Johannine authorship in his writings of around 110 CE. He refers to a John as being the author of the fourth gospel. However, there were two prominent men living in Ephesus with the name John: the Apostle John and another, John, the Elder. At the time, people did not have surnames but were known by their first or given name and their place of residence. An example of this can be seen at the end of the fourth gospel.
What is known about John the Elder is that he was a priest, implying that he had some degree of education. He was in a position to be familiar with the topography of Jerusalem and the surrounding region, more so than a fisherman from Galilee. An interesting suggestion that combines the two Johns “is that John the son of Zebedee’s preaching and/or writing may have been gathered by another and was finalized after his death by another John, John the Elder.”  A similar suggestion is that John the Apostle was the “witness” to the events surrounding the ministry of Jesus but that John the Elder wrote the gospel from the testimony of the Apostle John. Some even speculate that John the Elder was also a witness, but this is doubtful. Needless to say, the confusion arising from two men with the name John at the same time and place, both active in the early church, and questions of authorship of the gospel should not be surprising. Eusebius (275- 339 CE), bishop of Caesarea, supports Papias’ statements and also refers to the Apostle John, but, more importantly, he differentiates between an apostle who was a disciple of Jesus and an elder who was a second-generation Christian, whereas Papias does not make such a strong distinction. In his writings, Eusebius notes the burial of John the Apostle in Ephesus.
Irenaeus (130-202 CE), Bishop of Lyons, makes what is thought to be the strongest affirmation of Johannine authorship. In Against Heresies, Irenaeus notes that he knew Polycarp, who knew John the Apostle. The Muratorian Canon affirms around 180-200 BCE that the Apostle John wrote the fourth gospel. Dionysius, bishop of Alexandria (265 CE), confirms the Apostle John as the author. By this point in time, “the only exceptions to the general acknowledgement of Johannine authorship of the fourth gospel were the Alogoi, a group so called because they refused to accept this Gospel with the logos doctrine of its prologue.” 
Several factors raise questions concerning the authorship of John. Nothing in the New Testament is found telling of John ever living in Ephesus. However, nothing in Scripture precludes him from moving there after Pentecost. Also, we could interpret a passage from Mark 10:35-39 to mean that James and John were martyrs, but it is not known as a historical fact. Another possibility is an individual who had the same name as the Evangelist. Some suggest this person, in collaboration with John, compiled the oral traditions and other source material for the gospel. While not an eyewitness, he was nevertheless a disciple of the Apostle John. It is he who was with John during his time at Ephesus, C. K. Barrett suggests, who wrote the first twenty chapters of the gospel. Once this major portion of the book was complete, a group from within the Johannine community went in to edit the material and append the last chapter. It is this group to which the references to “we” refer.
A typical argument against Johannine authorship is that the gospel contains little in common with the Synoptic Gospels. This is rather weak, and it is easy to refute with the assertion that John has a different intent in writing his gospel than the authors of Matthew, Mark, and Luke. Others question how a Galilean fisherman could possess the social or political connections to gain admittance to the courtyard of the high priest. However, Zebedee, the father of James and John, did own his boat and was apparently a businessman with some financial and political influence. Mark 1:20 notes that Zebedee had several servants. The financial status of Zebedee increases the possibility that his family and the high priest were at least acquainted. A similar criticism is that a simple, uneducated fisherman from Galilee would not be able to write in such a theologically deep manner. To counter this argument, it is known that, at the time of Jesus, children went to Beth Midrash, the equivalent of our elementary school, and would receive at least rudimentary training in writing and reading. As a son of a successful businessman, it also seems likely he would have been taught to read and write Greek as it was the language of commerce. At the very least, John would have been conversant and literate in Greek.
Others claim that, while the author is a disciple, he is not one of the twelve apostles. Another protest is that the gospel is too different from Matthew, Mark, and Luke to be written by a disciple since all four gospel writers have the same source. This is a fallacy in that it assumes the disciples thought to remain together to coordinate their efforts and maintain a single purpose in writing their gospels. Others doubt Johannine authorship because the gospel makes no mention of the transfiguration, nor provides any details about Jesus’ prayer at Gethsemane. If John, as one of the three disciples closest to Jesus (Peter, James, and John), does not mention these significant events, critics claim he could not have written the gospel. To refute this suggestion, Morris notes that John “may have found it difficult to find a place for the transfiguration in a Gospel where one of the major themes is that Jesus’ glory was manifested continually in the path of lowly service and that it was preeminently shown on the cross. Where is there a place for the transfiguration in this scheme?”  As a note, John 12:27-28 does mention the time at Gethsemane, although not to the extent of the other gospel writers. Still another objection is that, according to Matthew, Mark, and Luke, all of the disciples fled when the authorities came to arrest Jesus. However, John's gospel notes the beloved disciple is at the home of the high priest and later at the cross of Jesus. A simple explanation is that John did join the others in the initial flight and later returned.
To conclude this brief analysis, there is sufficient reason to accept the premise that John is the author of the Gospel ascribed to him. While critics can question Johannine authorship, the preponderance of evidence coupled with the lack of credible opposition reasoning makes us conclude that he was, in fact, the author of the gospel as well as the writer of Revelation and the three small epistles that are given his name.