Many gospels were written, including and besides the four official ones. The four official gospels were written in Greece in Greek, the earliest (Marks') dating from the year 70 and the last one (John's) dating from the second century after Christ. (The oldest manuscript of the gospels that we found dates from the fourth century, but we have fragments that have been dated from the mid second century and we can deduct the date of composition from references in the texts). There is general agreement that three of the official ones (the "synoptic" gospels) derive from a common source (or Luke's and Matthew's simply derive from Mark's), whereas John's is inherently different. One hypothesis is that John's and this common source derive, in turn, from a pre-existing text, called "Q", that has never been found. One of the banned gospels, the gospel of Judas Thomas, has been considered a potential candidate for "Q" or for something closer to "Q" than anything else we have found.
John's gospel is markedly different from the other three gospels: it names many people who are anonymous in the other three gospels and it includes two episodes (the wedding at Cana and the raising of Lazarus) that the other gospels seem curiously unaware of. It "sounds" more knowledgeable: it provides details about the early proselytizing of Jesus and the rivalry between Jesus' sect and John the Baptist's sect. The account of Jesus' trial and crucifixion is more credible. Yet, John's gospel is unquestionably a later work than the other three official gospels.
It is also likely that the gospels as we know them have been heavily rewritten after they were originally written. Papias of Hierapolis in 110 talks of the gospel of St Matthew as a collections of oracles, not of miracles.
All four official gospels were written after Paul wrote his letters. Paul's letters are the oldest Christian documents. But Paul admits he never met Jesus and, in fact, his letters contain almost no reference at all to Jesus' lives.
Irenaeus (at the end of the second century) is the first Christian writer who mentions the dogma of the four gospels. Before him there is no mention of those gospels as being the only "good" ones. Justin Martyr (150) does not mention a New Testament, does not mention Mark, Matthew, Luke or John. On the other hand, he mentions the "memoirs" of the apostles, which could be the letters and the "gospels" attributed to Peter and others (mostly not recognized by the Church) besides the letters of Paul and the acts of the Apostles. In 170 Tatian admits he was working on a new gospel that would summarize all the other ones, thereby implying that Christians were still writing and rewriting gospels based on their own assumptions and preferences, not on historical facts. Also in the second century, Clement of Alexandria admits that two versions of Mark's gospel existed but one was being suppressed because it contained two passages that should not be viewed by average Christians (both passages could be interpreted as Lazarus being Jesus' lover and his "resurrection" as being an "initiation" to some kind of sexual rite, the way most pagan "mysteries" implied a death and a rebirth). Thus, the texts were being chosen, edited and purged for the first two centuries of the Christian era. That process had solidified by the time Irenaeus wrote that there were only four gospels.
Irenaeus' choice was formalized in 325 at the council of Nicaea, where those four gospels became the official dogma of the Roman Church and all other histories of Jesus were banned.
Irenaeus picked only a fraction of the available literature on Jesus. He excluded some of the most popular texts, such as the gospel of Thomas and the gospel of the Hebrews (by far the two most popular texts among early Christians). Either the memory was lost of what was old and what was new (Irenaeus claims that Mark and Luke were eyewitness which of course they were not) or the Church was already at work to completely reinvent the story of Jesus to suit whatever ideology. For example, if one wanted people to believe in Paul's letters, then he would probably choose those four gospels over all the other ones. The fact is that the dogma immediately ignited a very contentious issue.
Texts outlawed by Rome paint a very different picture of Jesus' teaching, especially the ones written by the "gnostic" Christians. Sometimes Jesus appears as a sort of communist revolutionary, sometimes as a sort of Buddhist thinker. In the most ancient texts he rarely appears as the Jesus who makes miracles and ascended to heaven, and sometimes does not appear at all. Sometimes he barely appears at all, while others (James, Paul) are the predominant characters. Peter, the most famous of Jesus' followers, is actually a very minor figure in early Christian documents.
Today, it is sometimes difficult to understand why some gospels were banned. Several of the banned gospels are apparently consistent with the dogma: why ban them? The devil is probably in the details: in 325 Christianity had become the religion of the Roman empire and it was not nice to emphasize that it was the Romans who had killed Jesus; in 325 Christianity had taken the beliefs that would become the Catholic dogma, and it was not nice to emphasize that Jesus had brothers (although even the official gospels say so) or that Mary Magdalene was always with him (although even the official gospels say so) and it was nice to undermine Jesus' miracles. Most of the gospels may have been considered redundant (they didn't add anything meaningful to the story) and dangerous (they could stress aspects of Jesus' story that the Church would rather downplay).
The gnostic Christians were persecuted after Rome converted to Christianity and most of their texts were burned. The church also outlawed all other histories of Jesus but the four official ones.