See ya never.
Clyde Decker is an amoral, cold-blooded, and corrupt CIA agent. His capabilities and reputation can be confirmed from the fact that he frightens John Casey. He first appears in the Season Four episode, Chuck Versus the Cliffhanger.
Decker contacts Chuck directly when he tried to break Volkoff out of prison to counteract The Norseman. Decker had already transferred Volkoff before Chuck's arrival at the prison. Decker then issues an arrest warrant to cover up any conspiracies with regard to Agent X.
While transporting Volkoff, Decker removes the faulty prototype Intersect from his brain before Chuck could access the man, reverting to Volkoff's original identity, Hartley Winterbottom aka Agent X. Once Chuck breaks into the transport, however, Hartley follows him after recognizing him as the son of Stephen Bartowski and creates a temporary measure to counter the Norseman poison. Decker is left in Volkoff's cage.
Decker eventually captures Chuck, Mary, Casey and Hartley outside Westside Medical and debriefs them at Castle. Decker removes the Intersect 2.0 from Chuck and attempts to convince Casey to tell the Bartowskis that the Intersect project is over. Casey figures out that Decker wants them to make a run for it so that he can look like the hero when he kills them. Decker assured him he had no trouble looking like a bad guy. Casey then got the jump on Decker and helped his friends escape.
When Chuck finally acquires the antidote for Sarah, Decker and a team of CIA agents were waiting outside Westside in anticipation of Chuck's return. Despite the fact there was no logical need to prevent her treatment, Decker was determined to stop Chuck, and felt that he had beaten Chuck when his agents outnumbered Team Bartowski and the CAT Squad. Chuck, however, was accompanied by Russian Spetsnaz units from Volkoff Industries and forces Decker to stand down. Chuck then promises to leak the truth about Agent X and Decker's involvement if he dares to harm his friends and family.
Decker has the entire Team Bartowski fired, Chuck, however, practically spits "I quit!" at Decker.
At the end of the season four finale, Decker reveales that everything that has happened to Team Bartowski had been part of a plan, and that Chuck was merely a pawn. The plan has many parts like Fulcrum, The Ring, Daniel Shaw, Agent X, The Omen virus and more. The main objectives of the plan is to eliminate Chuck Bartowski and his team. This is eventually shown to be only partially true.
In Chuck Versus the Zoom Decker foils Carmichael Industries as they attempt a heist on Roger Bale by freezing all not only the money involved in the con, but all of Carmichael Industries assets as well - leaving them with nothing but the Buy More and Castle.
Decker is a key member of a group of rogue CIA agents, tasked with bringing Chuck down. He issues a hit against Morgan in Chuck Versus the Business Trip, and then when that is foiled, has Casey arrested for murder when he takes out the assassins. Decker blackmails and coerces Chuck and the team into acquiring a computer virus when he threatens the life of the imprisoned John Casey. When he reneges on his promise to free Casey, and tells Chuck he is now in the frame for releasing the Omen, to ensure Decker won't be complicating anyone's life again, Gertrude Verbanski picks his pocket, taking the Omen and leaving a small explosive at the end of Chuck Versus the HackOff, Decker is killed by the blast. The CIA is offended by his murder, and the rogue team continue to send operatives against Chuck and his associates, until Shaw is finally captured and exposed in Chuck Versus the Santa Suit, where it is revealed that Decker was indeed corrupt and was blackmailed into organizing the 'get Chuck' campaign by Daniel Shaw. Shaw was able to manipulate Decker into hunting down Chuck and ultimately removing the Intersect 2.0.