The epistle of 3 John was written by the apostle of John. It is about four men: the apostle John, Gaius, Diotrephes and Demetrius. Diotrephes was a dictator in the church and the apostles teaches us how to deal with such a leader. in shape contrast Gaius and Demetrius are wonderful, godly men whom the apostle presents in contrast. You may be interested in visiting the 3 John Q&A archive.