Sometimes The Hero (or The Big Guy in their team) will face a large horde of Mooks and tell their leader he's going down. The leader will often say, "You and What Army?", then discover that the hero doesn't need one. This one man is the army and can go around killing thousands of enemies.
The One Man Army does far more than pull his own weight. Villains tend to underestimate this person at first, considering him Just One Man. They are quickly proven wrong. This is often justified by making the character a Super Soldier against mundanes, possessing far superior weaponry, or otherwise tremendously advantaged.
The damage to the psychological state of someone like this is not always considered. It certainly would be affected by taking so many lives away. The impact of this is lessened if the character is explictly a Living Weapon and/or if the enemies are Faceless Goons or don't register as human beings and therefore exist solely to provide a Mook Horror Show.
In a series aimed at younger audiences, they may simply defeat large masses of people rather than outright kill them. In playing this trope, it is useful to have The Evil Army try to Zerg Rush said character in The War Sequence. This trope caters to everyone's inner Munchkin; 99% of First Person Shooters ever made fall under this.
Often goes hand-in-hand with It's Up to You and Walking Armory. When the One Man Army is intentionally sent out to take care of the problem by himself, it's a case of One Riot, One Ranger. Compare and contrast Person of Mass Destruction, who's symbolically treated like a weapon by the setting, and Omnicidal Maniac, who is all too willing to push themselves into this territory. In the latter case, the Omnicidal Maniac often gains their kill-count through using WMDs on hapless civilians rather than personally fighting enemy combatants. Villains who are like this aren't bothered by Mook Depletion.
Being one of these qualifies you as a Crew of One (though not for a Big Badass Battle Sequence). However, very few people will respect your ability, or worse, seek to abuse it because "We Do the Impossible" is in effect. Contrast with the Badass Army where each individual could be considered this but are part of said army, as well as the Easily Conquered World where it's the severely, severely outnumbered enemies who are kicking ass and taking names. If one man makes the army, then you have The Minion Master. Likewise, if one man becomes the army, it's Me's a Crowd.
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- Real Life
- Multiple characters in Ravages of Time are able to hold their own against whole armies, such as Liaoyuan Huo and Zhang Liao. A special notice goes to Lu Bu who, with his daughter strapped to his back, tried to break through the siege of Xiapi; he was severely out-numbered but managed to take out all of Cao Cao's generals and was only defeated when he was absolutely exhausted.
- Several characters in God of High School are this, but very few can match Jin Mo Ri's feat of wiping out over 180,000 angels the size of skyscrapers in under thirty seconds after unlocking his power as the Monkey King.
- Played oh-so-straight when Sgt. Slaughter joined the ranks of G.I. Joe. The commercials were something else...
- Toa usually work in teams, but there are occasions where they manage to demolish small armies. One particular example that stands out is Kopaka defeating three dozen Zyglak offscreen. What makes this even more impressive is that Zyglak are almost immune to Elemental Powers which Toa usually use as their primary attack.
- Axonn and Brutaka are each worth a team of Toa by themselves, and together they once handled an army of Skadi warriors and only handicapped by the fact they were there to broker an alliance and thus not (intentionally) trying to kill any of them. A Skadi is usually about as physically strong as a Toa, for the record.
- The Makuta, however, take the cake thanks to their Combo Platter Powers and the fact they can literally spawn their own personal army of kraata and Rahkshi. Teridax once held his own and survived fighting odds of 100,000 to 1, albeit with his robot vessel beaten to a barely-functioning pulp by the end of it.
- He-Man, the Most Powerful Man in the Universe. Of course, he doesn't always fight the forces of evil by himself...
- Maji de Watashi ni Koi Shinasai! has many characters who can beat up masses of people by themselves. For instance, most of the named characters in the Kawakami War are essentially Hero Units.
- Abraham Van Helsing is the single toughest fighter the protagonists of Code:Realize have on their side. So much so that when they're attacked by multiple enemy airships in the anime, their solution is load Van into cannon and shoot him at the enemy. Van then proceeds to move from airship to airship, taking them out one after the other.
- Grisaia Series: Though the previous novels in the series handled protagonist Yuuji's capabilities with at least a touch of realism, by the end of Rakuen, when he assaults Oslo's base in the climax, he carves a bloody path through his private army, taking down 40-50 armed mercenaries.
- In Danganronpa 2: Goodbye Despair,Peko Pekoyama becomes one in her execution (which is even called "One-Woman Army" in English), taking down numerous Monokuma attackers armed solely with her sword. In the process, she accidentally slashes out Fuyuhiko Kuzuryu's eye.
- Hank from Madness Combat is perhaps the universal embodiment of this trope. In the flashes, he could kill a hundred guys in five minutes.
- Jebus also qualifies. As well as all of the fan-characters.
- CollegeHumor video "Video Game Boss Lament" has villains expressing shock to their minions at how a protagonist is able to get through them.
- Every. Single. Freelancer. Ever. from Red vs. Blue. Season 9 makes this very apparent.
- When sufficiently angered, Caboose can smash his way through dozens of soldiers. Problem is, he's Caboose, so he forgets how to get angry fairly often.
- In Episode 67 of The Most Popular Girls in School, Brittnay kills all four of The Expendables, in self-defense.
- RWBY: In the "Red" Trailer, Ruby Rose carves through a huge horde of demonic werewolves without taking a single hit. In Volume 3, Neopolitan infiltrates an Atlesian airship and slaughters all the soldiers on board, freeing Roman Torchwick and allowing him to hijack the ship.
- Dreamscape: Implied with Melinda, considering it took the entire population of her Mirror Universe to weaken her enough to seal her away, as seen in the flashback in "The Mystery of Melinda".
- Los Hermanos, a member of the Global Guardians, is literally this. He's a super-powered duplicator who can make thousands upon thousands of copies of himself.
- The Kriegan Army from Lambda. Each soldier is trained to take down dozens of enemies by themselves. Higher up, their elite Knights of Grabacr are up there at Person of Mass Destruction.
- In the pilot of Hogan Vs Flair, the card features the "Kevin Nash Burial Gauntlet Match". It's pretty much Nash just destroying one guy after another after another with his Jackknife Powerbomb, parodying the way the Real Life Nash would always insist on winning (and get his way most of the time.)
- Worm has quite a few, but the standout example is Contessa, who has singlehandedly delivered a Curb-Stomp Battle to a large group of people in every fight she's been in.
- As a result of the Mob's total inability to switch out Pokemon, some Mons in Twitch Plays Pokémon tend to fall into this category. Pidgeot ("Bird Jesus") from the first run is the primary example, but Feraligatr ("Lazor Gator") and Azumarill ("M4 Moe") also have this status.
- Galm comments on this when he plays Sniper Elite III: "I am the most interesting man in this world. We need like fifty of me."