Agree that it was the Apostle John. Over the years, I have read of how some attempt to discredit the Gospel of John because he wrote of things/events the other Gospels do not include. As well, MANY churches/denominations/movements do not adhere to some of what John wrote as being commandments from Christ.
John's Gospel, more than any of the others in my opinion, is the Gospel of Love. People can try to discredit it all they want, but it will remain the cornerstone account of the Gospel of Christ for me and my church.