Weng Weng. He was a martial arts movies actor. 83 centimetres tall (2'9").
Most short kendo practitioners. While the big guys may be able to hit harder, the smaller ones move faster and hit more areas, which is what counts in kendo. Case in point: a 5'1 man beating a 6'3 guy within ten seconds. Quite impressive.
Morihei Ueshiba, founder of Aikido. Many pictures of O-Sensei, as he is known, show him in the process of serenely◊ trouncing◊ people quite a bit taller and younger than him.
Nobuyoshi Tamura, former student of Ueshiba, sensei of the French Aikikai, an 77 years old quite small man (compared to his French and European student) who has no qualm about having his younger, taller and stronger students crawl to the ground.
Gozo Shioda, an early student of Ueshiba and founder of Yoshinkan Aikido, " was a small man, standing at around 5' 1" to 5' 2" (155–157 cm) and weighing around 102 lb. to 108 lb. (46–49 kg)", according to that Wikipedia page.
Muggsy Bogues managed to hold his own against the best basketball players in the NBA despite being 5'3" (160 cm) tall - the shortest man to ever play in the league. Bogues had several pictures of him with the tallest NBA player ever, the 7'7" (231 cm) Manute Bol. There was a 28-inch (71 cm) difference between their heights◊. Bogues and Bol were actually teammates for one season—Washington Bullets owner Abe Pollin was the Bill Veeck of the NBA.
Israel is one of the tiniest countries in the Middle East. It's also a well known military powerhouse.
Similar to the Israel example is Finland, Switzerland and (during the Cold War) Sweden. All nations with populations below 10 000 000 inhabitants and armed forces counting numbers close to the million.
Many combat specific soldiers are shorter, around the 5' range or less, and a Napoleon complex isn't uncommon. But in a Real Life aversion, it's a common complaint among drill sergeants in Combat Arms OSU Ts that 'the skinny ones break too easily', while the overweight recruits develop muscle mass from fat with fewer injuries.
Nepalis are known for their small size. Despite that the Gurkhas have a remarkable reputation as soldiers. During the 60s the Gurkhas usually carried the American M16, rather than the British SLR. The reason for this was that the M16 was lighter and easier for the Gurkhas to fire.
Audie Murphy At 166cm/5'6", the Marines and paras rejected him for being too short. His company commander tried to have him sent to a cook and bakers' school after basic, but he'd have none of it. He went on to win every military award (some multiple times) in the US up to and including the Medal of Honor. And a few French and Belgian decorations on top of all that (little trinkets like the Légion d'honneur). And he had malaria at the time.
Simo Häyhä, at 5'3'' (160cm), was likely the greatest sniper of all time. He is officially credited with killing 705 Soviet soldiers over roughly 100 days of combat.
The shrew is among the tiniest mammals in the world, and they can take down things that, proportionately, would ruin a wolverine's day.
Humans, too. 80 kg man can hunt almost any prey using tools. Without them, however, a man still can defeat an alligator or survive an encounter with a bear, if lucky. If you take account on the muscle mass, humans are incredibly strong.
While size does make a major difference among evenly skilled fighters in the martial arts scene, the smaller competitors are still formidable fighters capable of impressive feats; many ostensibly lower weight class fighters have fought in the heavyweight divisions and done quite well. Also, when weight classes were introduced to competitive judo, many of the small judoka left the sport, saying that building the skills to overcome larger opponents were an integral part of it.
Bruce Lee. The man was seriously tiny and scrawny for what was considered a good build for actionherobadasses. That really didn't stop him, and it was theorized that, pound for pound, he was probably one of the strongest men alive.
Chris Paul is one of the best and most feared players in the NBA, despite being one of the shorter ones.
Boxer Manny Pacquiao is 5'6", and tends to come weighing in the mid 140 pound area. He's one of the best boxers in the world. You can underestimate him because of his size, goofy smile and friendly manner if you want to, but he will fuck you if you do.
5'1'' MMA fighter Nakai Rin certainly counts.
Foil Fencers are often going to be better if they are both short and skinny, and they are harder to hit, and can get in close more easily. Short historical fencers who know that they're doing are nothing to sneeze at, either, when you realize that you have to bend at the knees (bending over exposes your head) to hit anywhere except for the head, which is far easier to defend against than your legs, which is their primary target.
Rhinoceros beetles. They are about 60 mm long, and can lift up to 850 times their own weight.
Liam Hoekstra: The world's strongest toddler. He has a rare genetic disorder that makes him have a (incredibly high) metabolism, and has 40% more muscle than the average kid. In short: he's three and has a six pack. How does that make you feel, nerd?
The Ratel, or Honey Badger, is an animal only three feet long. It is also the most feared animal in Africa. Honey badger don't give a shit about lions, cobras, etc. since their skin is thick enough to protect them against most animal stings and bites and actually too tough to be pierced by a spear or an arrow and it can withstand several machete blows, they have been known to chase away adult lions and steal their kills, they raid henhouses by actually tearing off the planks from their walls... short of actually being bulletproof, there is little they can't withstand.
Many small ice hockey players (David Krejci, who ended his career with the Boston Bruins, and Theoren Fleury, who most famously played for the Calgary Flames) can play a style better suited for players way larger. Krejci's hit opponents so hard, he gained the nickname of Wrecking ball.
Maurice Jones-Drew from the Jacksonville Jaguars. He was passed over in the draft until the second round because most scouts thought he was simply too short (he's listed at 5'7" and that's probably being generous). He's consistently been one of the NFL's top rushers, while spending most of his career on Jaguars teams that didn't have much else of anything in the way of offense.
Leopards are the smallest of the big cats, and not only kill animals that are bigger than they are, but have been known to drag carcasses twice their own weight into trees. See here for a leopard carrying a zebra nearly as big as itself straight up a tree and making it look totally effortless.
Philippine national hero Jose Rizal, author of Noli Me Tangere and El Filibusterismo, is only 1.5 meters tall. He is not only a polymath, but he is also a gym buff, a gifted fencer, a sharpshooter, and a wrestler. He challenged a bigger bully to a fight and won.
Machine example. The "FQ" series produces anywhere from 300 to 400 horsepower. The engine is a two liter straight-4. Most consumer level cars with that engine produce under 200 horse power.
Formula One engines are restricted to under three liters. They produce well over 600 horsepower.
Most modern turbocharged engines (as in "designed from scratch to be turbocharged", not as "someone added a turbo") are incredibly strong and also light for their size: VW/Audi 1.8T (it can be easily modified to run over 400hp), Subaru 2-liter boxer (even street versions kick serious ass, but it has been modified for drag racing to give a whopping 700 hp), Renault Megane RS 2-liter turbo and so on.
Peter Dinklage is a man with dwarfism, but he's also a hell of an actor.