"The Gospel of John illustrates what it looks like when God the Son comes to dwell among His people. John’s Gospel profoundly shows how God’s Son, Jesus, makes it possible for us to have an eternal relationship with God the Father (John 3:16–17).
The text of the Gospel of John identifies its author as a witness of Jesus’ crucifixion (19:35) and as the disciple loved by Jesus (21:20, 24). According to early church tradition, the author is the Apostle John, the son of Zebedee (also called John the Evangelist)—whom the early church fathers also regarded as the author of 1 John. However, the Gospel of John was originally anonymous, and thus it is possible that another church leader, whom the early church called John the elder, is the author or final compiler. Some church fathers thought John the elder might have been the author of 2–3 John, but others ascribed 2–3 John to the Apostle John (see the “Introduction to 2 John”). In addition, Revelation, may be ascribed to the Apostle John, John the Elder, or another John (see the “Introduction to Revelation”).
The Gospel was most likely written ca. AD 85–95, although if John the Elder is its author it could have been written in the early second century AD. The “Rylands Fragment,” a tiny piece of papyrus (about the size of a credit card), contains parts of John 18 in Greek and dates to AD 125–150."

—Faithlife Study Bible, Lexham Press