Wot Steve H said. Though I don't see any reason to doubt that the writer of 1 & 2 John was not the same one as the writer of the Gospel. There might be a case for 3 John, but I'm not convinced that this, too did not come from the same source. Since the 1 John and the Gospel are very close stylistically,and quotes from both survive from around AD 90, I have no problem that they were either written by, or dictaded by, the disciple John, brother of James.