The Acts of the Apostles introduces Simon as a magician already established in Samaria before the apostles arrive there, a man the text says the Samaritans called "the Great Power of God" and followed with something close to awe. When the deacon Philip preaches in the city and performs healings, Simon is baptized along with many others and, Acts says, was himself amazed at the signs he saw, attaching himself closely to Philip afterward.
The turn comes when the Jerusalem apostles Peter and John arrive to lay hands on the new believers so that they receive the Holy Spirit. Simon, watching the Spirit conferred through the apostles' touch, offers them money for the same power, asking that whoever he lays hands on might also receive it. Peter's rebuke is unsparing: "May your silver perish with you, because you thought you could buy the gift of God with money. You have no part or share in this ministry, because your heart is not right before God." Peter tells him to repent and pray for forgiveness, warning that he is "full of bitterness and captive to sin." Simon's reply in the text is not defiant but frightened, asking Peter to pray for him so that nothing he has said will come upon him, and the episode ends there, without recording whether he repented.
The exchange gave Christian tradition its word for the offense, simony, the buying or selling of ecclesiastical office, position or spiritual benefit, a term with a long afterlife in church law and controversy that far outran the brief scene in Acts that produced it. Nothing else in the canonical New Testament mentions Simon again.