Cypher Reagan was the hidden secondary antagonist in the Matrix.
He was a human released from the Matrix by Morpheus. But he hated the real world, and after nine year on the Nebuchadnezzar, he decided he had to get back into the Matrix.
He was portrayed by actor Joe Pantoliano.
History
When Morpheus believed that their next target, Neo, was the One, Cypher made contact with the Agent Smith. When Trinity was in the Matrix at the beginning of the movie, Cypher contacted her and enabled the Agents to trace the line, but Trinity got away.
Later on in the movie, after Neo was on the ship with them. Cypher went into the Matrix and met with Agent Smith in a restaurant. Cypher told Smith that he want to have his memory erased, and be reinserted into the Matrix, stating that "ignorance is bliss." He also said that he wanted to be someone rich and important, like an actor. Smith told him that Cypher could have anything he wanted, if he gave Smith the access codes to the Zion Mainframe. Cypher told Agent Smith that he did not know them, but Morpheus did. So the two of them made a plan to trap Morpheus.
When the crew went into the Matrix to visit the Oracle, Agent Smith, who had been told by Cypher the whereabouts of their hideout, organized a police squad. When the crew got back to their hideout to exit the Matrix, The Machines used a De ja vu to block their escape, then sent Smith, the other agents, and their squad in to catch them. Mouse was killed, and Morpheus was caught by Agent Smith and the police. The rest escaped through the walls. But Cypher, pretending to fall behind, was let out by the police, who knew he was on their side. He then took a short cut to the nearest Phone, and got out before the others. When Cypher was back on the ship, he took a lightning rifle, kiled Dozer, and wounded Tank before they could get the others out.
Cypher then answered Trinity's wireless phone and revealed his treachery. He than pulled Apoc and Switch's plugs, killing them. He wanted to save Trinity for last, because he still had a bit of love for her, so he went for Neo. Cypher tested Morpheus' theory that Neo was the One, saying that if what Morpheus believed was true, there would have to be a miracle to stop him from pulling the plug. Unfortunately for Cypher, Tank was not dead and he blasted Cypher with the rifle, killing him.
After Cypher's death, a group called Cypherites were formed. They hold the same beliefs as Cypher.