Star Wars: Clone Wars has varying degrees of this trope. Durge is shown (and explicitly stated in other EU material) to be a one-man arsenal, but "only" kills a few dozen soldiers. General Grievous is similarly able to cut through clones and Jedi with his usual psychopathic zeal, but his body count is relatively low. Anakin and Obi-Wan are better examples, a "body count" of droids well in the thousands, but they have their limits and still rely heavily on the armies they command. Mace and Yoda, however, wipe out hundreds of droids without their lightsabers and tear apart entire legions with little help from their soldiers.
In Star Wars: The Clone Wars, the special mention goes to Yoda who gets into a contest with Asajj Ventress over whether a certain planet will join the Republic or the Separatists. If he can escape Asajj's best Separatist droids, the planet will go with the Republic. Yoda barely breaks a sweat. Asajj then tries to attack Yoda in a rage and he casually extinguishes her dual blades using the Force then Force-pulls them from her grasp.
King Katuunko: You were right, Count Dooku. One Jedi is not worth a hundred battle droids... more like a thousand.
Jedi Master Mace Windu: "My name is General Mace Windu of the Jedi Order. At this point of the Clone War, I have dismantled and destroyed over 100,000 of you type one Battle Droids. I'm giving you an opportunity to peacefully lay down your weapons, so that you may be reprogrammed to serve a better purpose than spreading the mindless violence and chaos which you have inflicted upon the galaxy." (Star Wars: The Clone Wars: "Unfinished Business")
The whole Team Avatar is this to some degree. In the episode "Earth King", this group of kids in age from 12 to 15 year old, just blast to the Earth King's Palace through a legion of elite earthbenders.
Iroh is explicitly described as a "one man army" after he escaped from prisoner during the Eclipse, fighting off the entire guard, while no one was able to firebend.
Likewise, Bumi managed to liberate the city of Omashuby himself. He didn't run from the army. The army ran from him.
According to the Word of God, the reason Piandao is so revered as a sword master is because of what happened when he decided he was tired of the military and became a recluse. The military sent a hundred soldiers. Piandao sent them all back. And he can't firebend, either.
Then we've got Ty Lee, the butt-kicking, GenkiDark Action Girl, who takes out an entire group of elite earthbenders by herself in "The Drill".
The Order Of The White Lotus is basically composed of these. The previously mentioned Iroh, Bumi, and Piandao are all members. There's a reason their battle with a Fire Nation army that was a Curbstomp Battle.
Lin Beifong manages to free her officers from an Equalist base, doing practically all of the work.
Much like the original Team Avatar, the members of the Red Lotus are incredibly powerful, and all 4 combined have come out ahead while massively outnumbered. Their leader is somewhat less powerful, even after becoming an airbender.
Kuvira is shown to be one when she curb stomps a group of about twenty bandits single-handedly.
In GIJoe, Sergeant Slaughter was known to defeat whole squads of Mooks by himself. But that's not all. When he was put in charge of training the other Joes, he challenged them to attack him all at once. They took him up on it, and he won without breaking a sweat. (Of course, his Real Life counterpart likely isn't this tough, but still...)
Megas XLR. First episode: On one side, Coop and a nameless sidekick mecha. On the other, a large army of alien mooks and their commander.
Kiva: Look at them all. These odds are awful. Coop: You're right, it is kind of unfair. * knocks sidekick out* Now it's fair.
In Invader Zim, it's shown that apparently a single competent Irken Invader is capable of conquering a planet by themselves. Helps that they do have some impressive technology at their disposal. The main character has even better technology that he's engineered himself, but being a Chaotic StupidGenius Ditz has no way to use them effectively (though he's still pretty dangerous at times).
The title character of Samurai Jack, with only a couple prepared traps, single-handedly destroyed hundreds (if not thousands) of Kill Bots in the third episode.
Not only that, but the last few Kill Bots actually took a step backwards trying to running away. Jack said "No, there is no escape." and demolished them.
At least once, he managed to beat a moderately large army of robots with literally no effort at all.
In "Birth of Evil", Aku becomes a literal example, splitting himself into an army of man-sized duplicates of himself in armor. (However, seeing as Jack's father still defeated them all, he qualifies for the Trope here as well.)
Ashi, the only surviving Daughter of Aku, takes down an entire army of Orcs, who are after Jack's head, using martial arts and turning their own weapons against them.
Brock Samson, or as he's been referred to by The Monarch, the Swedish Murder Machine.
In Teen Titans, Robin, definitely. In Apprentice, he takes down a whole army of Sladebots by himself, brutally, and in the second part of the season finale, he takes down his entire team. By himself again. When they were all attacking at once. And it's a Curb-Stomp Battle.
In fact in "Winner Take All", the Master of Games literally introduces him as a "One Man Army".
Alice of Superjail! is the only guard in a demented facility full of the very worst psychopaths not fit for regular prison. And she has no trouble kicking all their asses, and keeping the prison in relatively normal condition.
Tai Lung in Kung Fu Panda has his own prison and is guarded by one thousand guards as well as being held completely immobilised. When he gets free of his shackles, he beats up all the guards in a matter of minutes. Granted, he finishes the job with some dynamite that sends a large number of them flying at once; it might have taken up to another minute or so otherwise.
In one of the Season 5 finale's Bad Futures, however, he uses an actual army to conquer the rest of Equestria. Albeit out of pragmatism instead of weakness, though; he easily defends himself from any Royal Guards that attempt to attack him directly.
Each of the Mane 6 qualify in their own right; together, they were able to take on a good chunk of the changeling army after it invaded an entire city:
Twilight is the personal protégé of Princess Celestia, perhaps the most well-read unicorn in history, and the Element of Magic. And then she becomes an alicorn princess. She's one of the most powerful characters in the series.
Applejack is only an Earth Pony, and not even the strongest one in the series (Maud Pie), but she is tough enough and stubborn enough to defeat hordes of enemies.
Rarity is a less powerful unicorn than Twilight, but she's shown martial arts proficiency, and is nearly as fierce as AJ in combat.
Fluttershy is normally kind and quiet. But don't make her angry. She's stronger and faster than she looks, and is the group's resident Beast Master. She also has a special ability called The Stare which basically forces whoever she's using it on to do what she wants.
Rainbow Dash is pretty much the definition of Awesome Ego, but she has the skills to back it up. She's the fastest flyer in Equestria, is the only pony in history to preform a Sonic Rainboom, and also has a black belt in karate. She's strong enough to apparently lift- and fly around with- a boulder several times her size, and she can smash through a pillar of rock with little problem. As a Pegasus, she can also manipulate clouds and weather to her advantage. She's almost as stubborn as Applejack and is usually the first to resort to violence.
Family Guy: In "The D in Apartment 23", Chris and Meg are confronted at their school cafeteria after Brian posts an offensive tweet, and they proceed to take down the entire student body by themselves (the scene itself being a spoof of the church scene from Kingsman: The Secret Service).
Rick and Morty: In the third season premiere, "The Rickshank Redemption", Rick Sanchez single-handedly brings down the Galactic Federation and the Council of Ricks, the two most powerful organizations in the show, by teleporting the latter's headquarters into a Federation prison, then devastating the Federation's economy.