Judas

As I understand Christianity it is the death of Christ on the cross that atones for all sins. The resurrection is also important, but the actual crucifixion.

Billy Graham has said "Jesus’ death on the cross is important because without it we would have no hope of forgiveness or eternal life. " 

"The Pope has said “Salvation comes only from the cross, from this cross where God was made flesh. There is no salvation in ideas; there is no salvation in good will, in wanting to be good. No! The only salvation is in Christ crucified because only he — like the bronze serpent — was able to take upon himself the poison of our sin and heal us.” 

I could multiple examples, but I think this suggests that my understanding of it is approximately right.

The Romans crucified Jesus and thus did all Christians a big favour, apparently. But the one guy who made it all happen is seen as a "traitor". I'm speaking of Judas who sold Jesus to the Romans for 30 pieces of silver. On the one hand, sure, it's a betrayal and I get that at the time people might have been miffed. But the crucifixion became the centrepiece for the whole religion, the rationale for redemption, and provided Christians with both their most enduring symbol - the cross.

If Judas had not sold Jesus down the river, he might have escaped custody. Judas facilitated the most important moment in the history of Christianity since the nativity.