The Gospel of John was supposedly written by the Apostle John, a son of Zebedee and the brother of James the Apostle. Some controversy exists regarding the authorship of this Gospel because it supposedly was not written at the same time as the other three Gospels.
The Gospels of Matthew, Mark and Luke are called the Synoptic Gospels because they recount many of the same stories in much the same sequence. The Gospels of Matthew and Luke are thought to have been taken in part from the Gospel of Mark. The Gospel of John was written in about 70 A.D., much later than the other Gospels were written. John's Gospel seems to be independent of the other Gospels.
Another controversy related to the authorship of the Gospel of John revolves around the Book of Revelation, also thought to be penned by the same John. Some historians note that the authors of the two books of the Bible may not have been the same person because, although written in Greek, the two books were not written in the same style.