Read the Bible - Gospel of John, Chapter 14.

The most important fact about the author of the Gospel of John is that he was an EYEWITNESS to everything he has written about. John was possibly one of the "Sons of Thunder" or the sons of Zebbedee, James and John. He was, possibly, as young as 14 or 15 years old when Jesus called him. It is known that he lived until the 90's of the first century. He had been exiled to the Isle of Patmos, where he had the vision and wrote the Book of Revelation. It is known that when he left Patmos, he retired to Ephesus, where he died. One of his most famous disciples was Polycarp. One thing that is very evident from reading this Gospel is that the author was, most certainly a Jew. He displays an intimate knowledge of Jewish customs, festivals and beliefs. He has a detailed knowledge of the geography of Palestine, suggesting that he was a native of that area. Today, John is known as Saint John, the evangelist.