Judas Iscariot
There are several explanations as to why Judas betrayed Jesus. In the earliest account, in the Gospel of Mark, when he goes to the chief priests to betray Jesus, he is offered money as a reward, but it is not clear that money is his motivation. In the Gospel of Matthew account, on the other hand, he asks what they will pay him for handing Jesus over. In the Gospel of Luke and the Gospel of John, the devil enters into Judas, causing him to offer to betray Jesus. The Gospel of John account has Judas complaining that money has been spent on expensive perfumes to anoint Jesus which could have been spent on the poor, but adds that he was the keeper of the apostles' purse and used to steal from it.
John 13
Jesus quotes the words of Psalm 41:9:
According to the Pulpit Commentary, in the Psalm, "Ahithophel (who had been a counsellor to King David) is almost certainly intended", and the Cambridge Bible for Schools and Colleges notes that "the words of the Psalm are not a direct prediction, but the treachery and the fate of Ahithophel foreshadowed the treachery and the fate of Judas". The Jerusalem Bible translates this verse as "Someone who shares my table rebels against me" (John 13:18). Francis Moloney identifies this verse not only with Judas' betrayal of Jesus, but also with Peter's denial of Him (John 18:15-27).