Exploring the First Epistle of John
There has been some disagreement over the years about who wrote the First Epistle of John, was it the same person that wrote the Second and Third Epistles? Certainly there are some similarities, but also differences, and the second two could well have been written by a member of John's community. However, if we assume that the First Epistle is written by John the Apostle, the son of the fisherman Zebedee, who was one of the first to be called by Jesus, then you might want to look at the first five verses of the Gospel of John, and see if you can find any similarities with this letter.
What can you find out on-line through your search engine, about the Apostle John, after Jesus' death? Be aware there has always been a lot of "stories" about John, and you need to be aware that a lot of these may just be legends.