When The Flash made its debut on The CW, it joined Arrow to help create the new DC world known as the Arrowverse. The show brought along with it something Arrow wasn't known for: heroes and villains with superpowers. Specifically, the heroes and villains on Flash were known for their speed, and so the Speed Force was born.
However, when Supergirl arrived, new speedsters were added to the world. With Legends of Tomorrow, some of The Flash's speedy characters made their jump to that show as well. Now, there are a ton of people running around The CW and its Arrowverse at impossible speeds. But who's the fastest of all?
Wally West
In the comic books, Wally West was the Flash for an entire generation of fans. The version on The Flash is very different. He's the son of Joe West, a street racer who studied engineering and high powered engines. He wanted, more than anyone on the show, to be a speedster.
When Wally got his powers, it was a dream come true. What makes Wally impressive is that the sky is the limit for him. When he began to master his powers, he was faster than Barry Allen was when he first started. There is a chance that, one day, Wally will be the fastest of them all. For now, though, he ranks below many of the other speedsters in the Arrowverse.
Jay Garrick
Meeting the real Jay Garrick on The Flash was a very cool thing for a few reasons. First of all, he is the Earth-3 doppelganger of Barry's dad, Henry Allen, which gave John Wesley Shipp a nice change of pace after serving the first couple of seasons in prison. Second, Shipp played Flash on the classic TV show from the 90s, so this was a return for someone older fans had seen before.
Third, Jay Garrick is the original Flash from DC Comics. On the TV show, he was able to catch up to Barry Allen in the Speed Force (to try to stop him from changing the timeline), but he was beaten by Savitar. He was also beaten by Zoom, so he's not as fast as others.
Jesse Quick
Jesse Wells is the main Flash on Earth-2, and just so happens to be the daughter of Harrison Wells on that Earth. She gained her powers when Barry Allen was trying to get his own back: a dark matter pulse struck her, eventually allowing the Speed Force connection.
She came to Earth-1 to work with Barry, Wally and the heroes here, but has since returned to her own Earth to lead her own superhero team. She has more stamina that Jay Garrick, due to her younger age, but was not as durable as Barry. She ran faster than Wally on the show and held her own against Savitar for a short time.
Supergirl
Moving out of the world of Flash, Supergirl ranks next on the list. The question of who is faster between Superman and Flash is one that a lot of fans like to ask, but what about Superman and Supergirl? It was proven on Supergirl that she is actually stronger than Superman: she knocked her cousin unconscious when the two fought.
However, their speed levels have never been tested against each other. When she raced Barry, she lost, proving that he is faster than she is -- although she admirably kept pace. At the same time, Flash and Superman have raced to a tie, so it is assumed that Superman is faster than Supergirl.
Superman
While Superman sits right above Supergirl in this rating (due to their individual races against Barry Allen), there is a chance that Supergirl is actually faster than her cousin. She already proved to be stronger than he is, after all. Still, until proven otherwise, these are the rankings.
The fact is, Barry Allen beat Supergirl in a race and tied with Superman. However, if Barry is to be believed, he could have beaten the Kryptonian if he wanted to. Barry claimed he did this to entertain the crowd, so if that is the case, Superman is much slower than the Fastest Man Alive in the Arrowverse.
Zoom
Hunter Zolomon was Zoom, possibly the scariest villain that Flash and his friends ever faced. Zoom showed from the start that he was more powerful than anyone on Team Flash, and moved so fast that Barry Allen had trouble catching up to him.
There was even a moment where Zoom stole Flash's powers and grew even faster than Barry Allen. Even after Barry got his powers back, the two raced and Zoom was still faster than Barry. Of course, the end came when Barry finally caught and beat Zoom, leaving him ranked a little lower here -- although a change to Hunter turned him into something even faster.
Savitar
Savitar is Barry Allen from an alternate future, so considering he is an older Barry, it is obvious that he is very, very fast (since Flash just gets faster as he gains experience). Here is the twist: when Savitar is inside the Speed Force, he is the fastest speedster in existence. However, when he comes out of it, he loses a lot of his speed.
Inside the Speed Force, Savitar beat Jay Garrick, Wally West, and Barry Allen at the same time. In his alternate future, he was even known as the God of Speed. Once he came out into Barry's world, he was a basic speedster and eventually fell to Team Flash.
Reverse Flash
Many villains have appeared on The Flash throughout its run, but no-one has matched up to Eobard Thawne -- the Reverse Flash. He was the villain in Season 1, and made quite a name for himself: masquerading as Harrison Wells, gaining the trust of Barry Allen, creating most of the metahumans on Earth-1 and then almost destroying Flash for good.
He is also a genius and was able to create devices to help make him even faster than anyone alive -- putting him on an even playing field with Barry Allen. However, Barry beat him in the end, and there is someone other than Allen that has Thawne darn frightened, meaning that Reverse Flash ranks no higher than third.
Barry Allen
They call him the Fastest Man Alive, and that is true. When it comes to living beings, there is no-one on any Earth that is faster than Barry Allen -- the Earth-1 Flash. He has beaten almost everyone in races and his speed makes him more powerful than almost anyone in a fight.
Barry beat Savitar, Reverse Flash, Zoom, and countless others, proving over and over again that his mastery of speed trumps all. Cisco has remarked on more than one occasion that Barry runs faster than anyone they ever encountered, and the scary thing is that he gets faster and faster as the need arises. Only one being in existence has proven to be faster than Barry Allen.
Black Flash
While Barry Allen is the Fastest Man Alive, there is one being that is faster than he is. That would be Black Flash. Remember when we mentioned that Hunter Zolomon turned into something even faster? After Zolomon died, he was given the mantle of Black Flash by the Time Wraiths.
His job is to hunt down and eliminate any speedster in the multiverse who attempts to mess with time. Given this job by the Time Wraiths, he ended up faster than anyone. He started on a mission to hunt down Reverse Flash, and then was able to catch Barry Allen in season 3. Barry only survived because the Speed Force allowed him to.