Author: John 21:20-24 describes the author as "the disciple whom Jesus loved," and for both historical and internal reasons this is understood to be John the Apostle, one of the sons of Zebedee (Luke 5:10).
Date of Writing: Discovery of certain papyrus fragments dated around A.D. 135 require the book to have been written, copied, and circulated before then. And while some think it was written before Jerusalem was destroyed (A.D. 70), A.D. 85-90 is a more accepted time for its writing.
Purpose of Writing: John 20:31 cites the purpose as follows: "But these are written that you may believe that Jesus is the Christ, the Son of God, and that believing you may have life in His name." Unlike the three synoptic Gospels, John's purpose is not to present a chronological narrative of the life of Christ, but to display His deity.