Can your character kick-ass despite working in a Dry-Cleaners? Do they have strange, unexplained tattoos and gnarly scars littered across their bodies? Do inane things cause traumatic, immobilizing flashbacks? Where did they get those Cool Guns and how the hell do they know how to use them all?
When all of these qualities fit the profile of your character, then they may or may not have been involved in a form of military or law-enforcement services and have since moved on to other things. One does not just forget these skills and may have to use them when they are needed. The reasons they have kept their past professions a secret and why they continue to do so can be for many reasons, maybe out of a sense of guilt for their on-duty actions or because they feel like it is not worth explaining. Either way, all we can do is guess.
The invention we refer to as "the Military" is a multifaceted socio-political organization that has one purpose: search and destroy. Oh, and to serve and protect their country. And provide tuition for its members. And instill discipline into those who have none. To describe the purpose of a military is a philosophical debate unto itself, but this also has to keep in mind the various divisions and branches (Army, Navy, Air Forces, Marines, etc) and their types (artillery, infantry, special forces, etc).
This isn't just something that applies to a specific military organization either. It can work under homeland intelligence services like the Central Intelligence Agency (CIA), international agencies like the International Criminal Police Organization (INTERPOL) and any other Government Agency of Fiction that has Fun with Acronyms.
- The Night Unfurls: Other than being a Hunter of Monsters, nothing in Kyril's past explicitly suggests he had been in some form of military. Nevertheless, Kyril has displayed remarkable expertise in many tasks that involves the military, especially during situations where he is in charge in the battlefield. Said tasks include but not limited to: leading troops into battle, maintaining overall morale, instilling discipline, and knowing when and which places to deploy his company.
- Oversaturated World: Because Classified Information is usually connected to governments and militaries, from Unfriendly Compeition - Dark Crystal, when Lyra asks Bon-Bon how her dad learned to do a sleeper hold.
"Where'd you learn how to do a sleeper hold, anyway?"
"My dad taught me."
"Where'd he learn it?"
- Walter Sobchak in The Big Lebowski makes it very clear in every scene that he has done service in Vietnam, but it is never made clear in which branch of the military he served. While the Army, the Navy, the Marine Corps, and the Air Force were all involved, over half of the troops involved were a part of the Army, so it is likely that Walter was in the Army. But if the original screenplay is in any way canon, Walter did not actually serve any time in Vietnam, thus averting the premise entirely.
- Frank Martin in the Transporter movies served under an unspecific branch of the British military.
- Planet Terror: El Wray is an expert with guns and blades and is the best fighter of the whole group, but the Sheriff refuses to give him a gun because of his criminal shenanigans in the time he'd met him. Once the plot re-starts after apologizing for the missing reel, El Wray has given the sheriff his secret past (but the audience doesn't gets to hear it) and the sheriff is incredibly awed by him ("I knew your name was 'El Wray', but I didn't knew you were that 'El Wray'",) hands him a firearm and lets him carry on. His interaction with the colonel afterwards implies that Wray was part of some kind of black-ops division or at least saw military service.
- Brother (1997): The protagonist Danila repeatedly claims that he has sat out the First Chechen War in a desk job at some command post but, when guns are drawn, displays skills of a seasoned veteran of close quarters combat and urban warfare, easily outclassing the criminal thugs who come after him or his brother.
- Star Trek: Deep Space Nine has Garak. Garak, the plain, simple Cardassian tailor who is only a tailor and not an Obsidian Order spy at all.note
- Shepherd Book from Firefly has a suspicious level of knowledge about guns for a preacher, and is implied to have a former connection with the Alliance. Eventually confirmed in the Expanded Universe comics.
- Ian Chesterton from the original Doctor Who is unusually good at different sorts of violence for a science teacher. In one episode he mentions that he "trained as a fighter" but this isn't expanded on. Fanon often assumes he served some National Service (required military service of most British men his generation), but this is never confirmed onscreen.
- Mass Effect: Andromeda: Liam was a cop on Earth, and then joined Crisis Response, neither of which involved heavy combat training. When questioned by most party members about his surprising skill in skirmishes, he says he learned how to fight "in movies." One party member, Drack, calls "Bullshit" and demands to know what war veteran taught him how to fight. Liam admits to him that he had a mentor in Crisis Response that taught him how to fight, but that's as far as he's willing to reveal.
- Phil Cassidy from the Grand Theft Auto games is alleged to have served in the army in some games, but others say they doubt this in others. Notably, he claims to have lost his arm in combat in Grand Theft Auto III, but Grand Theft Auto: Vice City shows he lost it due to an accident with explosives.
- Played for Drama in Knights of the Old Republic II: The Sith Lords. You meet Atton Rand in jail where he's ostensibly being held for contraband smuggling. He's got a smart mouth and a blaster, and is apparently over his head when it comes to Jedi-Sith matters. But several characters remark that his fighting style is not what you'd expect out of a typical spacer whose combat experience is limited to Bar Brawls. Atton is evasive about it until you get a chance to confront him. He used to be a Jedi hunter and Torture Technician in Revan's army, converting Jedi by making them succumb to The Dark Side but hauled ass when one of his targets showed him that he was Force Sensitive and about to be on the other end of the torture rack.
- The Dunkel parents in El Goonish Shive are very good at organising a search-and-rescue mission, doing so with at least as much military precision as the characters we know are government agents would have. They are a stay-at-home mom and possibly an accountant. Word of God is that there is absolutely no intention to explain this.
- It is implied that Karl Copenhagen and Quinn from Demo Reel may or may not have been members of the East German secret police and the IRA respectively. Ask and they'll deny it.
- Barbara Lake from Trollhunters knows Krav Maga, an aggression-based martial art that is commonly practiced by military personnel. Since the only visual instance of one of her relatives - her brother or father - is a photograph of him in an army-green mess dress tuxedo with medals pinned to it, it is likely that she served some form of military service just like he did, or at least worked as a military M.D. at one point in her life.
- Smiling Friends: The Boss seems to handle an M16 assault rifle in the midst of a giant mental breakdown far better than most civilians would, handling it both during running (against chest, barrel pointing up), breaking through doors (crashing through rather than opening) and aiming (keeping Grim in the sight even as he falls to the ground) like he's been trained for it. There's no other indication that the Boss has seen military service, so it may just be part of one of the show's subtler Running Gags in portraying every firearm with far more realism than anything else.