Ever since Jay Garrick inhaled hard water fumes and became the first Flash eighty years ago, DC's Scarlet Speedsters have faced a great number of supervillains with an endless array of powers, gadgets, and magical abilities. From low-level crooks who took their game to near-omnipotent beings obsessed with destroying all of reality, there's no form of evil a Flash hasn't taken on.
And while there have been a fair amount of stinkers in the Flash's rogues gallery, be they baddies who went after Jay, Barry Allen, or Wally West, there have also been a great number of all timers. The Flashes have run into battle against villains who would even make Superman shake in his boots. The most famous speedsters in comics have traded blows with some of the most powerful and vile characters to ever grace the four-color page.
10 Vandal Savage
An immortal being, Vandal Savage has faced off against almost every superhero in the DC Universe, including all three Flashes. But it was his battles with Wally West - the third Flash - that really showed off what Savage could do. Along with being the first villain Wally faced off against when he took up the Flash mantle, Savage helped create Velocity-9, a highly addictive drug that gave normal people super speed. Savage flooded the streets with V9, leading to some serious problems for Flash. In their third and final battle, Savage kidnapped all of Wally's loved ones and nearly killed the hero.
9 Captain Cold
Leonard Snart was a smalltime criminal when Barry Allen - the second Flash - first showed up on the scene. After the Fastest Man Alive stopped one of his break-ins, Snart found himself sitting in prison with a lot of free time and decided to put his mind to use. After reading an article that theorized that the energy emissions of a cyclotron could interfere with the Flash's speed, Snart taught himself how to build a cyclotron gun that he could use against Central City's hero.
After testing his gun and finding that it could freeze objects or people, Snart took on the name Captain Cold, and the rest is history. While he may not be the strongest villain Flash has ever faced, his street smarts have always kept the speedster on his toes.
8 Mirror Master
A member of the Rogues, a team of Flash villains led by Captain Cold, Mirror Master has one of the most dangerous weapons in the DC Universe, a mirror gun that allows him to open up a portal to the Mirror Universe. Through the Mirror Universe, Mirror Master can travel to any place in the universe as long as there's something there that has a reflective surface.
Along with the ability to enter the Mirror Universe, Mirror Master can use his tech to create lifelike illusions, hypnotize people, or even turn them into glass. Luckily the villain, like the other Rogues, sticks to a strict rule against killing, but if he ever chose to break that rule, things could get very messy very fast.
7 Abra Kadabra
Making a living as a magician in the 64th Century was proving very difficult for Abra Kadabra. No matter how many rabbits he pulls out of his hat, Kadabra's gags just weren't as impressive as the technology of the time. Searching for an adoring audience, Kadabra stole a time machine and traveled back to current day Central City where he was sure people would love his tricks. When no one appreciated his art, Kadabra decided to use his future tech against them, and in turn, he became one of the most dangerous foes any Flash has ever faced off against.
6 Kilg%re
An electro-mechano-organic intelligence from the Pleides Sector, Kilg%re came to Earth after destroying its own planet and being trapped in a vibrational limbo by Meta#sker. While running tests on his speed at a S.T.A.R. Labs facility in the flats near Salt Lake City, Flash accidentally freed Kilg%re from its limbo. In a matter of days, Kilg%re had taken over the electrical systems of every city and town in the United States, and it would have taken over the world if not for some quick thinking by Flash and Cyborg.
Kilg%re later returned by taking control of Linda Park, but was now looking to help Flash. Kilg%re even saved Flash's life when Vandal Savage tried to kill the hero. Since then, the alien being has returned to its evil ways but rarely shows itself to the world.
5 Gorilla Grodd
Coming from the secret society of Gorilla City, Gorilla Grodd is a super-intelligent superpowered gorilla who has been a major problem for the Flashes for years. Grodd once used his ability to telepathically connect to all animals to start a "pet revolution" that led to dogs, cats, and every other animal in Keystone City rising up against the humans. The only thing that stopped Grodd's plan was Flash, Vixen, and Rex the Wonder Dog. Most recently, Grodd worked with Lex Luthor and the Legion of Doom to help bring Perpetua back from near death, leading to the destruction of all of reality, as seen in Dark Nights: Death Metal.
4 Savitar
Claiming to be the "God of Speed," Savitar only faced off against the Flash once, but he left a wound as deep as the greatest villains the Scarlet Speedster has ever dealt with. Savitar escaped from the Speed Force and came back with the ability to give and take away superspeed from others. He used this ability to kill the Russian speedster Cassiopeia, a member of Kapitalist Kouriers as well as to take away the powers of most of the Flash Family. In the battle to stop Savitar and his speed ninjas, Johnny Quick, one of the first speedsters in DC Comics, was pulled into the Speed Force, never to be seen again.
3 Reverse-Flash
The greatest villain of any Flash, Eobard Thawne, the Reverse-Flash, has made it his life's mission to unleash as much pain as he can on the Flash Family. Coming from the far future and obsessed with Barry Allen, Reverse-Flash has gone so far as to kill Barry's mom and his wife Iris West. When he wasn't busy killing the people Barry Allen loves, Reverse-Flash worked quietly in the background, manipulating the lives of the other speedsters in the DC Universe, causing rifts in the Flash Family that almost tore them apart. The damage Reverse-Flash has done, especially to Wally West who he pushed into committing murder, may never truly heal.
2 Dr. Alchemy
Albert Desmond is a genius chemist who wants nothing more than to create things that can make the world a better place. Alex Desmond is a criminal mastermind who wants nothing more than to destroy the Flash. These two men exist in the same body, and when Alex takes control, things get very scary.
Using the Philosopher's Stone and calling himself Dr. Alchemy, Desmond has one of the most dangerous weapons in the universe. He can quite literally transmute any substance into any other substance, meaning that if he so wished, Dr. Alchemy could turn all the oxygen on Earth into gold, instantly killing everyone. Luckily, he has never gone that far.
1 Anti-Monitor
In the 80 years that DC Comics has been publishing Flash comics, there has only been one villain who was able to cause the death of a Scarlet Speedster; the Anti-Monitor. In the classic series Crisis on Infinite Earths by Marv Wolfman and George Perez, the Anti-Monitor has captured Barry Allen and keeps him docile with the help of Psycho-Pirate. When Barry is able to break out of Psycho-Pirate's hold, he sacrificed himself to destroy the Anti-Monitor's antimatter cannon that was set to destroy the last five Earths of the Multiverse. It took the full force of every hero and villain in the DC Universe to defeat the Anti-Monitor, but they wouldn't have had a chance without the Flash giving up his own life to slow down the galactic monster's plans.