He was the only non-Galilean among the disciples. His role in the band of followers was that of treasurer. He always watched out for the 'bottom line'. Some would call him an opportunist because he was always looking for ways to 'cash in' on his position and association with Jesus and the other disciples.
Judas was a covetous man—using his place as treasurer to dip into the common purse for himself. After he helped the religious leaders find and arrest Jesus, he realized the outcome of what he had done. He tried to return the money The priests didn't accept it because they considered it 'blood money'.
Judas reacted to the Priests' refusal by throwing the coins at them. He couldn't bear the guilt of what he had done. We all know Judas' outcome. We also know he could have gone to Jesus and asked forgiveness.