As with many Biblical characters, details of Judas are sketchy. Some scholars now doubt that he even existed, for Paul, the earliest New Testament writer, does not mention him by name. Further, throughout Christian history, his character has been used by Christians as part of their anti-Semitic stereotype of greed and treachery, so some suspect that the character of Judas was later created to justify this prejudice.
Even the exact meaning of his second name is mysterious, as it has been interpreted to mean that he was from a place called "Kerioth," or that he was a member of the armed opposition to Rome (using a "sicarius," a dagger, as a weapon). The legend that he had red hair has also been connected to "Iscariot," relating it to the Aramaic for "red." Some suggest the name is a later addition, related to the Hebrew for "false one" or "betrayer," thereby building Judas' role into his name.
The one act Judas is known for - "betraying" Jesus to Roman authorities to be put to death - is now also regarded as highly debatable. The Greek term can be more neutrally rendered as "handed over," as though Judas merely facilitated a meeting between Jesus and the authorities, with no ill intent, and without certain knowledge of the outcome. Some even now interpret Jesus' words to him as a command to "hand him over" (Matt 26:50; John 13:27), so that Judas' act would actually be one of obedience to Jesus, not betrayal of him.
If Jesus did not command Judas to "hand him over," then what were Judas' motives? Again, the Bible is ambiguous, and the different gospel accounts do not agree on all the details. Some of the gospels mention payment for this act (Matt 26:14-16; Mark 14:10-11; Luke 22:3-6), but this motive is not consistently emphasized, and some think the amount too insignificant to motivate such a close follower to turn against Jesus. Some have taken hints in the gospels (Matt 10:34; Mark 14:47; Luke 6:15; 9:54) that some of Jesus' disciples advocated violence against Rome, and connect Judas to this supposed activity. They go on to speculate then that his "betrayal" of Jesus may have been out of frustration with Jesus' pacifism, or even an attempt to force Jesus to act violently. With no Biblical basis, but with great detail and excitement, some hypothesize a love triangle between Jesus, Judas, and Mary Magdalene (sometimes including a homosexual liaison between Judas and Jesus), with Judas' jealousy then providing the motive for betrayal.
Whatever Judas did, his subsequent fate is another point of divergence between the Biblical accounts. In Matt 27:3-10, we read that Judas returns the money he had been paid, and then goes and commits suicide by hanging himself. The money is taken and used to buy a potter's field in which to bury the unidentified and destitute; this field is called "The Field of Blood." But in Acts 1:16-20, Judas himself buys a field with the money he had been paid, but subsequently falls down, bursts open, and dies. (The detail that he fell from the roof of a building is commonly added to this account, to make it seem more likely that it would cause such extensive bodily damage.) The field is then called "The Field of Blood." The story in Acts is similar to a non-canonical version in which Judas contracts some horrible disease that makes him swell until he bursts open and dies. Attempts to harmonize these accounts are frequent, right down to the present.
Recently, the Gospel of Judas was published to great fanfare. This gospel had previously been known to us only from a reference to it in the writings of Irenaeus (ca. 180). The Gospel of Judas is a fascinating witness to the beliefs of gnostic Christians (a very popular group that broke off from mainstream Christianity in the 2nd century), but it is unlikely it was written by a contemporary of Jesus, and completely impossible to prove such an attribution.