John authored the second most books in the New Testament.
He refers to himself as the disciple that Jesus loved.
He lived the longest of all the disciples.
Jesus gave him responsibility for Mary (Jesus’s mother).
His gospel is unique from the other three.
He is more focused on the mystical aspect of Jesus. He doesn’t just state the facts, but really draws our attention to the spiritual aspects of Jesus as God rather than the human aspects of Jesus.
John
John - Blue Letter Bible: NASB95
Introduction to John - Blue Letter Bible: ESV Global Study Bible Introduction