Who is the disciple that lay his head on Jesus' bosom in John chapter 13 verse 23?
In the fourth gospel, this was the "disciple whom Jesus loved". We do not know who the "disciple whom Jesus loved" was meant to be. Irenaeus identified him as being John, a view that is still held by conservative Christians today, and drew the conclusion that John was the author of this gospel, which had previously been anonymous. This was speculation and, today, most scholars doubt that the author really was John.
A consistent theme of John's Gospel is that Peter was always compared unfavourably with the "disciple whom Jesus loved". It seems likely that the real author of John was troubled by the reverence given to Peter, and wanted to portray him as no more than a disciple, so as to get the focus back on Jesus. He did not want to create another personality cult in place of that of Peter. By choosing an anonymous disciple, he ensured that this disciple coud not be worshipped. By calling him the "disciple whom Jesus loved" he made it clear that there was a disciple much greater than Peter, without appearing to disparage Peter. The scene in John 13:23 serves to emphasise the affection that Jesus felt for this disciple. So, the "disciple whom Jesus loved" is likely to have been no more than a literary invention.