Cypher is a fictional character from the movie The Matrix played by Joe Pantoliano.
His full name is Louis Cypher or Lou Cypher (pronounced Lucifer), although he was referred to as "Mr. Reagan" by Agent Smith.
Cypher is one of the rebels from Morpheus' hovercraft the Nebuchadnezzar. His character is bald and he has a moustache. After betraying the rest of the crew to the machines, Cypher is killed by Tank.
His choices in the real world raised a lot of questions for philosophers: would you stay in the harsh real world, or the excellent dream world. Knowing that he is a traitor, his name Cypher may mean the 30 denarius received by Judas Iscariot for betraying Jesus.
See also: The Matrix character names