Every story needs a villain and Judas Iscariot fills this role in the gospels. He is the apostle who betrays Jesus and helps the Jerusalem authorities arrest him. Judas may have enjoyed a privileged position among Jesus' apostles -- John describes him as the band's treasurer and he is often present at important times. John also describes him as a thief, but it seems implausible that a thief would have joined such a group or that Jesus would have made a thief their treasurer.
Some read Iscariot to mean "man of Kerioth," a city in Judea. This would make Judas the only Judean in the group and an outsider. Others argue that a copyist error transposed two letters and that Judas was named "Sicariot," a member of the party of the Sicarii. This comes from the Greek word for "assassins" and was a group of fanatical nationalists who thought that the only good Roman was a dead Roman. Judas Iscariot could have been, then, Judas the Terrorist.
Judas Iscariot is known as the companion of Jesus who betrayed him -- but what and how did he betray? That isn't clear. He points out Jesus in the Garden of Gethsemane. This is hardly an action worthy of payment because Jesus wasn't exactly in hiding. In John, he doesn't even do that much. Judas doesn't actually do anything except fulfill the narrative and eschatological need for the Messiah to be betrayed by someone.
Judas Iscariot filled a necessary literary and theological role in the gospels by betraying Jesus. Someone had to do it and Judas was picked. It's questionable whether Judas even acted of his own free will. There was no option for Jesus not to be executed because without his crucifixion, he could not rise again in three days and thus save humanity. To be executed, though, he had to be betrayed to the Jewish authorities -- if Judas hadn't done it, someone else would have.
Since Judas Iscariot did something so critical and necessary for Jesus' mission, why is he reviled? Why isn't he also a saint? If Judas loved Jesus as much as the other apostles, wasn't his job much harder than theirs? According to John, Jesus said "Greater love hath no man than this, that a man lay down his life for his friends," but didn't Judas do something very similar by sacrificing himself and his reputation in order to help Jesus fulfill prophecy?
Read More: Judas Iscariot the Apostle