In episode 10 of season 3, "Chuck Versus the Tic Tac", Colonel Casey was dismissed, adopting his cover of an overaged retail electronics salesman as his life.

While serving there, Casey was informed that he had not qualified to train with Special Operations Command, and immediately after receiving this news was recruited into the NSA by Colonel James Keller.

"Chuck Versus the Tic Tac" reveals that Casey served in the Marine Corps as Alex Coburn and had a fiancée named Kathleen McHugh.

When Casey is dismissed from the NSA by Beckman, Chuck tries to persuade him that all is not lost and that it is not too late to make amends for the past now that he is a civilian because Kathleen lives around town and he can finally get to know his daughter.

He shot Bryce during his escape attempt, apparently fatally, but not before Larkin was able to successfully send the contents of the Intersect to his old college roommate, Chuck Bartowski.

[12] He meets with a very personal betrayal when he discovers his old mentor and sensei, Ty Bennett, had turned rogue and is building a criminal empire with former students, even inviting Casey to join him.

However, this changes when Ned Rhyerson, a Fulcrum agent posing as a frightened amateur criminal, takes the Buy More hostage as a setup to discover what the CIA and NSA were protecting there.

[16] After failing his spy training, Chuck is dismissed from the agency, and Casey appears ready to pull out of Burbank without any mention of execution orders.

Goya addresses Casey as the man that saved Costa Gravas from civil war and leads him from the nuclear control room to the palace where he had a more fitting reward for the Angel of Life.

In the end, Keller is taken down, Kathleen is saved, and instead of going to prison for treason, Beckman gives Casey a something of a "second second chance", dismissing him from the Marine Corps and NSA service, and allowing him re-enter civilian life without his pension.

After Chuck announces his intentions to win Sarah back first before making any other decisions, Casey agrees to join forces with Morgan and Devon to help.

The mission nearly ends disastrously when two Interpol agents coming to take the prisoner into custody are revealed to be members of the terrorist ETA, but Casey and Morgan are rescued by Chuck and Sarah.

After the mission, Casey personally vouches to General Beckman for Morgan's role in locating Chuck and Sarah and his decisive actions in securing the Basque prisoner.

Interviews with Josh Schwartz and Chris Fedak at San Diego Comic-Con 2009 have indicated Casey's role will develop from strictly a protector to take on aspects of a mentor/student relationship with Chuck.

[27] Confusion throughout the series over Casey's branch of service was resolved in "Chuck Versus the Angel de la Muerte," when he both identifies himself as a Marine and the letters USMC are clearly visible stamped on his dog tags.

"Chuck Versus the Tic Tac" had previously supported the theory that Casey was a Marine officer, and his recruitment into the special forces is depicted in a flashback.

Although in "Chuck Versus the Angel de la Muerte" he mentions having attempted to assassinate Premiere Goya at Beckman's personal orders on several occasions in the early 1980s (once as early as 1982) and further admitted pride in the number of Goya's men he killed fighting against the Communist revolution in Costa Gravas, the name "John Casey" did not even appear in the government's records until 1989.

[18] Despite the humor, the unavoidable reality is that Casey is a killer and experienced assassin who has no compunction about solving problems with violence, often has difficulty distinguishing the value of human life, and seems to enjoy the prospect of killing a little too much.

In a bonus feature in the season two DVD, Casey instructs how to become a deadly spy, starting with shooting two guys who were talking off-camera and ending with advice on getting a second job during down time and advocating the elimination the other applicants ('... so go out and find a goat.

He also vouched for Sarah's father and suggested his assistance in helping them apprehend a Saudi sheik with terrorist ties should be considered when Jack Burton was to be brought to trial for his own illegal activities.

However he is also loyal to his government, and when it was sufficiently explained to him that leaving Chuck alive would place the country in danger, he was prepared to carry out his instructions regardless of his personal feelings.

[31] He keeps a photo of former President Ronald Reagan in his apartment which he has a habit of saluting and addressing directly as "Sir," is a Republican,[7][21] and has a "Rogues Gallery" he uses for target practice, including pictures of Adolf Hitler and Osama bin Laden.

A significant amount of humor in the series centers around Casey's demeanor and random moments that are completely incongruous with his tough image, such as unexpectedly singing a note to which a puzzle is keyed and revealing having been a choir boy with perfect pitch, and dancing to 1990s music (specifically Hanson's "MMMBop") while undercover as a DJ at Sarah's high school reunion.

[35] While working at the Buy More in the days leading up to Christmas 2008, Casey had been assigned to man the gift-wrap counter and was so distraught over the resulting paper cuts that he had band-aids on all his fingers.

He frequently responds to situations with monosyllabic grunts, which Chuck can recognize and has even numbered,[31] and often tosses off one-liners reminiscent of cliché action films,[21] sometimes quoting Baldwin's own previous roles.

He told Jane Bentley in "Chuck Versus the Masquerade" that he had no intention of leaving Burbank, indicating that Castle would be the terminal assignment of his military career.

Morgan, Casey and Devon refuse to let him back down, The trio borrow Jeff's spy gear-equipped van to kidnap Chuck and stakeout Sarah and Shaw on a date.

Meanwhile, Casey is still largely paralyzed by his dismissal and initially unwilling to help when Morgan and Chuck arrive to enlist him in their off-book operation to save Sarah.

The importance Casey puts on loyalty and honor is a catalyst for his growing fondness of, and respect for, the eccentric, juvenile and essentially untrained Morgan Grimes.

[18] It is revealed in "Chuck Versus the Subway" that Casey has re-established contact with his daughter, Alex, and is a regular visitor to the diner in which she works although she is unaware of his identity.