In The Matrix, the crew member who betrays the group is Cypher.
Cypher is a member of the Nebuchadnezzar’s crew and has spent years helping Morpheus search for the prophesied “One.” Unlike Neo, Trinity, and Morpheus, Cypher becomes deeply resentful of life outside the Matrix. He finds the real world bleak, physically difficult, and far less pleasurable than the simulated reality he abandoned.
His betrayal is revealed when he secretly negotiates with Agent Smith. Cypher agrees to help Smith locate and eliminate the crew in exchange for being returned to the Matrix, where he wants to forget that the real world ever existed. During a meal with Smith, he famously chooses the illusion of a satisfying steak over the knowledge that it is simulated.
Cypher is often confused with Agent Smith because both oppose Neo and the crew, but they are not equivalent. Smith is an autonomous program enforcing the Matrix, while Cypher is a human resistance member who knowingly betrays his allies. His name also evokes the word “cipher,” suggesting secrecy and hidden meaning.