The New Testament includes four books describing the life, death, and resurrection of Jesus: the Gospels of Matthew, Mark, Luke, and John. They were written in the first century; the earliest copies of them in our possession come from the middle of the second century. Christians have considered them the authoritative accounts of the events surrounding Jesus ever since they were written.
In the first few centuries following the death of Jesus and the Apostles, other “gospels” began to circulate as well. Some such “gospels” were written by well-meaning but ultimately misguided Christians who used them to try to fill in perceived “gaps” in the Gospel story: discussing Jesus’ birth and childhood in greater detail (like the “Protoevangelium of James”) or providing greater detail into the story of Jesus’ death and resurrection (as in the “Gospel of Peter”). Most such stories relied on the original four Gospels for information and provided additional speculation to explain or reinforce various doctrines and practices (contra 1 Timothy 1:3-4). These “gospels” are understood to be pseudepigraphic, later books written as if they had been written by a famous or notable person in the past. No one believes that Peter had anything to do with the Gospel of Peter, or that either James the Apostle or James the Lord’s brother had anything to do with the Protoevangelium of James. Most Christians in those days knew that those books were written later and did not consider them authoritative like they did the Gospels of Matthew, Mark, Luke, and John.
Another group of “gospels” were modified or written by the Gnostics. The Gnostics were various groups of people in the first few centuries of this era who believed in a mixture of Jewish, Christian, and Greek ideas. There was great variety in belief among various groups of Gnostics, but they all claimed to have received a superior sense of understanding and knowledge over “regular” Christians (the word Gnostic comes from the Greek gnosis, meaning “knowledge”). The Gnostics attempted to communicate this “superior knowledge” through manipulations of the stories and sayings of Jesus. Some of these books, like the “Gospel of Thomas,” are clearly based on the Gospels of Matthew, Mark, Luke, and John, share a lot in common with them, but feature additions to or manipulations of what Jesus said. Others, like the “Gospel of Truth,” the “Gospel of Judas,” or the “Gospel of the Egyptians,” prove radically different in tone and message from the four Biblical Gospels.
The Apostles Paul and John warned believers about the Gnostics, condemning their departures from the truths about Jesus revealed in the one true Gospel (cf. Colossians 2:1-10, 1 Timothy 6:20-21, 1 John 2:18-25, 2 John 1:6-11). Christians in the second century and afterward became aware of these Gnostic “gospels” after they were written and themselves wrote condemning their messages as false (cf. Irenaeus’ Against Heresies, Hippolytus’ Refutation of All Heresies, etc.). As with the other “Gospels,” so with the “Gnostic gospels”: no one really thought that the Apostle Thomas, or Judas, or any other Biblical character wrote them. Christians understood that these were later works derived from and/or speaking against the Gospels of Matthew, Mark, Luke, and John.
Perhaps you have heard about books “banned from the Bible” or about stories “the church doesn’t want you to hear.” These “alternative” gospels lay behind these sensationalist claims used to sell books and ignite controversy. Some of these “alternative” gospels might be new to us today, but they were well-known in the ancient world and rejected for good reason. Just because a story is called a “Gospel” does not mean that it was written by someone acquainted with Jesus or His earliest followers or that it belongs in the Bible!
Paul warned the Galatians to not accept any other gospel than the one they originally received from him, even if an angel from heaven were to announce it (Galatians 1:6-9). We do well to heed the same advice. The truth regarding Jesus’ life, death, and resurrection is found in the Gospels of Matthew, Mark, Luke, and John, and not in any other “alternative” gospel.