All of the 893 Pokemon officially released at the moment have their own sets of stats. These amounts, of course, can be worked on and improved according to how the Pokemon are caught and trained. And the numbers themselves involve Attack, Defense, HP, Special Defense, Special Attack, and Speed.
Speed is a value that establishes which Pokemon will go first during battle. Therefore, the higher Speed stat of the two or the three or the four battling Pokemon takes the first turn. (Unless the Pokemon uses a move like Quick Attack.) Then, subsequently, the next fastest Pokemon acts.
Updated September 28, 2021 by Erik Petrovich: The fastest Pokemon in the Pokemon franchise don't always take an aerodynamic appearance - some of the Pokemon with the highest Speed stats come as a surprise to many players. Ninjask, for example, is the fastest non-legendary Pokemon introduced all the way back in Ruby and Sapphire versions, while Mewtwo outranks some of the sleekest Pokemon throughout the series. It's an important stat to pay attention to, as Pokemon in these upper tiers of Speed will attack first more often than not, setting foes off-rhythm and allowing the player to control the battlefield.
15 Tapu KoKo
Tapu KoKo is an Electric-Fairy dual-type Pokemon introduced in Pokemon Sun and Pokemon Moon, with a description in Ultra Moon that reads "the lightning-wielding guardian deity of Melemele, Tapu KoKo is brimming with curiosity and appears before people from time to time."
With a base 130 Speed Stat, it's a Pokemon that will more likely than not strike before the opponent.
14 Crobat
Crobat is a Pokemon first introduced in Pokemon Silver and Gold versions for the Gameboy, and with the description in Pokemon Black that reads "having four wings allows it to fly more quickly and quietly so it can sneak up on prey without its noticing."
It is an evolution of Golbat, and its base 130 Speed Stat puts it on-par with some of the series' fastest offerings, despite coming from one of the series' worst Pokemon, Zubat.
13 Mewtwo
Mewtwo is the OG legendary Pokemon, introduced all the way back at the inception of the franchise. According to Pokemon Sword, Mewtwo was "created from the DNA of Mew," and is a "dangerous combination of overwhelming power and a savage heart."
It has a base Speed Stat of 130, leaving Mewtwo behind some other legendary Pokemon but far ahead of the majority of the competition.
12 Aerodactyl
The Fossil Pokemon Aerodactyl was first introduced in Pokemon Red and Blue versions, and is described in Pokemon Black and White versions as "a Pokémon that roamed the skies in the dinosaur era. Its teeth are like saw blades."
Like many of the Pokemon at this high tier of speed, its base Speed Stat is at 130, making it the fastest fossil-based Pokemon and among the fastest Pokemon in the series.
11 Jolteon
Jolteon is, of course, a Pokemon only attainable when the player uses a Thunderstone on an Eevee, and is just one of the many evolutions of the cute Pokemon. Introduced at the start of the Pokemon franchise, Pokemon Emerald version describes the Pokemon as able to "generate weak power that is amplified by its fur's static electricity to drop thunderbolts."
Jolteon has a base Speed Stat of 130, putting it ahead of any of the other evolutions (or, rather, Eeveelutions) of the Pokemon Eevee.
10 Barraskewda
According to Pokemon Shield, "It spins its tail fins to propel itself, surging forward at speeds of over 100 knots before ramming prey and spearing into them." That is a lot of knots, which makes sense considering Barraskeda enjoys a base Speed Stat of 136. It is a literal torpedo, earning the title of fastest Water-type Pokemon.
Barraskedwa is based on a barracuda, of course. And it is not too hard to figure out that its name is a combination of "barracuda" and "skewer." Arrijyda evolves to Barraskedwa at level 26, and they were bought introduced in Generation VIII.
9 Dragapult
According to Pokemon Sword, "When it isn't battling, it keeps Dreepy in the holes on its horns. Once a fight starts, it launches the Dreepy like supersonic missiles." These Dreepy missiles are not the only things that are supersonic, Dragpult itself achieves a base Speed Stat of 142.
It is not just the quickest Dragon-type Pokemon, and not only the speediest Ghost-type Pokemon, but also the fastest pseudo-Legendary. Dragapult is a floating salamander with a built-in aircraft catapult in its head, like a stealth bomber. The name itself is quite literally a combination of "dragon" and "catapult."
8 Zeraora
According to Pokemon Ultra Moon, "It approaches its enemies at the speed of lightning, then tears them limb from limb with its sharp claws." The speed of lightning is not an exaggeration, Zeraora boasts a base Speed Stat of 143.
Design-wise, it is a little tiger powered up by electricity. Zeraora's name is a mystery but could be a combination of Zeus, the Greek god who controls lightning and thunder, and "tora," which is Japanese for "tiger." Debuting in Generation VII, Zeraora is a strong addition to most teams, especially since it can also learn a few Dark and Psychic-type attacks.
7 Accelgor
According to Pokemon Sword, "It moves with blinding speed and lobs poison at foes. Featuring Accelgor as a main character is a surefire way to make a movie or comic popular." Move aside, The Flash, because Accelgor has a base Speed Stat of 145.
In case it was not obvious already, Accelgor's design is inspired by ninjas, racers, slugs, and snails. Even Accelgor's name is a combination of "accelerate" and "escargot" ("snail" in French). A Generation V creation, Accelgor can be obtained by trading a Karrablast for a Shelmet, causing the latter to evolve into the speedy Bug-type.
6 Zacian
According to Pokemon Sword, "Now armed with a weapon it used in ancient times, this Pokemon needs only a single strike to fell even Gigantamax Pokemon." When in Crowned Sword form, Zacian moves fast enough to only need a single strike when...striking...thanks to its base Speed Stat of 148.
Even though it is the heaviest Fairy-type Pokemon, Zacian is the quickest Fairy-type Pokemon as well as the speediest Steel-type Pokemon. Of course, it is based on a wolf but coupled with King Arthur (and the sword Excalibur) maybe. On the other hand, Zacian's name may simply come from "the cyan."
5 Electrode
According to Pokemon Alpha Sapphire, "One of Electrode's characteristics is its attraction to electricity. It is a problematical Pokemon that congregates mostly at electrical power plants to feed on electricity that has just been generated." After consuming enough electricity, Electrode legitimately moves at the speed of light with a base Speed Stat of 150.
In fact, it is the fastest Electric-type Pokemon. Electrode is a living Poke Ball, just like its pre-evolution Voltorb. But the name is a combination of "electric" and "explode," reflecting its ability to self-destruct in battle. Electrode's other stats might be somewhat average, but its incredibly high Speed makes it a capable Pokemon.
4 Calyrex
According to Pokemon Shield, "Legend says that by using its power to see all events from past to future, this Pokemon saved the creatures of a forest from a meteorite strike." The reason Shadow Rider Calyrex was able to rescue all those creatures is that it has a base Speed Stat of 150. This is the genuinely highest amount when it comes to all the Ghost-type Pokemon.
Regarding design and origin, Calyrex draws inspiration from arctic hares and crowns; whereas Spectrier is a ghost horse. Calyrex's name is a combination of "calyx" (Latin for "bud") and "rex) (Latin for "king); whereas Spectrier's name is a combination of "specter" and "destrier" (a medieval warhorse).
3 Pheromosa
According to Pokemon Sun, "One of the dangerous Ultra Beasts, it has been spotted running across the land at terrific speeds." Terrific speeds are an understatement, Pheromosa maintains a base Speed Stat of 151. Among all the Fighting-type Pokemon, it stands on top in this area.
Pheromosa probably is based on a cockroach, but not ugly. The name itself seems to be a combination of "pheromone" and "formosa," which is Portuguese for "beautiful."
2 Ninjask
According to Pokemon Omega Ruby, "Ninjask moves around at such a high speed that it cannot be seen, even while its crying can be clearly heard. For that reason, this Pokemon was long believed to be invisible." That's right, Ninjask, which enjoys a base Speed Stat of 160, is basically invisible while in motion.
It holds three high scores as a matter of fact: fastest Bug-type Pokemon, quickest Flying-type Pokemon, and speediest non-Legendary. Clearly, Ninjask is an insect but more specifically a cicada (with ninja qualities). Its name is, obviously, a combination of "ninja" and "mask." A Generation III Pokemon, Ninjask is born from a Nincada.
1 Deoxys
According to Pokemon Emerald, "A Pokemon that mutated from an extraterrestrial virus exposed to a laser beam. Its body is configured for superior agility and speed." Speed Forme Deoxys was created to be the fastest, quickest, speediest Psychic-type Pokemon ever. More importantly, though, it bears the highest base Speed Stat of all Pokemon, period.
In terms of design and origin, Deoxys is an alien that gets inspiration from the nucleic acid double helix and chromosome packages. Its name not only draws influence from deoxyribonucleic acid, but it is also quite actually and literally an abbreviation of DNA.