The gospel of John ends with (NIV) John 21:
20 Peter turned and saw the disciple whom Jesus loved following them.
As usual in this book, Apostle John refers to himself as "the disciple whom Jesus loved" in 3rd person singular:
He was the one who had leaned back against Jesus at the supper to ask, “Lord, who is going to betray You?”
24 This is the disciple who testifies to these things and who has written them down.
The author has just identified himself.
And we know that his testimony is true.
Who are the "we"?
25 There are many more things that Jesus did. If all of them were written down, I suppose that not even the world itself would have space for the books that would be written.
Who is this "I"? If this refers to Apostle John, this is the first and the last time, the author used the first person singular to refer to himself.
Does John 21:20-24 indicate that the original author of the Fourth Gospel was dead?
Was the Beloved Disciple the author of the Fourth Gospel?
Who was the Beloved Disciple?
I assume Apostle John is the author.