See ya never.
Clyde Decker was described as the CIA's toughest agent, the man sent to kill the men ordered to kill. He was first appearing in the Season Four finale episode "Chuck Versus the Cliffhanger". His capabilities and reputation can be ascertained from the fact that he frightens John Casey.
Season Four Edit
Decker speaks directly to Chuck when the latter tried to break Volkoff out of prison to counteract the Norseman. However, Decker already transferred Volkoff before Chuck's arrival and he fires Chuck from the CIA. Decker then issues an arrest warrant to cover up any conspiracies with regard to Agent X.
Later, Decker removes the faulty prototype Intersect from Volkoff before Chuck could hijack the transfer truck, returning Volkoff's original identity as Hartley Winterbottom and Agent X. Nonetheless, Hartley follows Chuck after recognizing him as the son of Stephen Bartowski and creates a temporary measure to counter the Norseman.
Decker eventually captures Chuck, Mary, Casey and Hartley outside Westside Medical and debriefs them at Castle. There, 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. He then got the jump on Decker and helped his friends escape.
Later, Decker and a team of CIA agents were waiting outside Westside in anticipation of Chuck's return after he acquired the antidote from Vivian Volkoff. Decker felt that he had beaten Chuck when his agents outnumbered Team Bartowski and the CAT Squad. However, Chuck brings in Russian Spetsnaz units from Volkoff Industries and forces Decker to stand down. Chuck then promised to leak the truth about Agent X and Decker's involvement if he dared to harm his friends and family.
Decker has the entire Team Bartowski fired, Chuck, however, practically spits "I quit" at Decker.
The Plan Edit
At the end of the season four finale, Decker revealed 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.
In "Chuck Versus the Zoom" Decker foils Carmichael Industries as they attempted 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 bring Chuck down. However, at the end of "Chuck Versus the HackOff", Decker is killed by Gertrude Verbanski. In "Chuck vs. the Santa Suit", it was revealed that Decker was indeed corrupt and was blackmailed into being his agent by prisoner, Daniel Shaw. Through this, Shaw was able to manipulate Decker into hunting down Chuck and ultimately removing his Intersect 2.0.
Decker blackmails and coerces Chuck and the team into stealing a computer virus when he threatens the life of the imprisoned John Casey, but this is his last slip-up, as Gertrude Verbanski takes steps, to ensure Decker won't be complicating anyone's life again by way of a small explosive.
While disavowing all knowledge of his illegal activities and persecution of Team Bartowski, the CIA is offended by his murder. The rogue team continue to send operatives against Chuck and his associates, until Shaw is finally captured and exposed.