There were a lot of contenders for this list of the best Flash villains, because countless enemies have tried to stop the red-and-yellow clad speedster in the last 50+ years.
But despite the hordes of villains that have tried to run down the Fastest Man Alive over the decades, these 10 villains stand out from the pack as the Flash's most iconic foes.
Glider is one of the biggest beneficiaries of a full-scale reimagining among Flash's Rogues.
Having begun life as Golden Glider, a villainous ice skater, Brian Buccellato and Francis Manapul's reimagining of Lisa Snart as an intangible mastermind, able to possess people, and clad in one of the coolest costumes from the 'New 52' era, elevated the character to a place she never could have gotten before.
Lisa Snart also appeared on several episodes of CW's The Flash, where she possessed a gun that turned people into gold, going by her original moniker, Golden Glider.
9. Pied Piper
Pied Piper might be higher on this list if he hadn't spent so much time waffling between heroism and villainy.
Indeed, Harley Rathaway is one of the most complex villains to cross Flash's path. Despite having challenged Barry Allen as a villain on numerous occasions, Piper eventually reformed, becoming close friends with Allen's successor, Wally West.
Though he's been something of a hero, or at least an anti-hero, for quite some time, he's gone back to villainy a few times over the years.
8. Captain Boomerang
Captain Boomerang may be more than a little goofy, but when you get past his boomerang pajamas and his little hat, he's kind of emblematic of what Flash's Rogues are all about.
Digger Harkness is a hard-luck criminal with little idea of what to do with his throwing skills and boomerang collection than to strap them to some crazy gadgets and start hurling them at the Flash. Step 3 of that plan is 'profit,' but darned if Harkness has any idea how to reach that goal. But that never stops him from trying, and even sometimes succeeding in some pretty villainous stuff, like killing Tim Drake's dad.
Captain Boomerang also appeared as a member of the Suicide Squad on Arrow, and appeared in the Suicide Squad live-action film, along with its upcoming sequel.
7. Weather Wizard
Who but Weather Wizard could challenge the combined might of Superman and the Quik Bunny?
But seriously, One of the things that makes Mark (or Marco, since the 'New 52') Mardon such a great villain is his crossover appeal. His weather manipulation abilities make him one of the most powerful Rogues, and having challenged at least three Flashes - even playing a part in the death of Bart Allen - he's also proven his chops in ways few others have.
But he's also challenged Superman, the Justice League, and served on numerous villain teams, making him not just a great Flash villain, but a great villain all around.
In fact, he's so great, CW's The Flash has gone to the well with him not once but twice with two different characters.
A former test pilot who was struck by lightning while flying an experimental plane (sentences like that one make comics awesome), Savitar found himself with strange Speed Force related powers and began building a cult around his abilities.
Savitar gained his powers in the '40s, pitting himself first against Johnny Quick and Max Mercury, who thought him defeated after Mercury abandoned him in the Speed Force. Savitar later reappeared, discovering his cult had grown while he was lost in time, and challenged Wally West - whose speed Savitar could not steal.
After Savitar's defeat at the hands of West and his allies, Savitar was once again stuck in the Speed Force, until returning to challenge Barry Allen and becoming a victim of the Reverse Flash's entropic sabotage of Allen's powers which caused Savitar to age into dust.
5. Mirror Master
The original Mirror Master, Sam Scudder, was a master of illusion, using his mirror gun to vex and addle the Scarlet Speedster at every turn. One of the more gruff members of the Rogues, Scudder's abilities were a product of his own ingenuity.
A lifelong criminal, Scudder became obsessed with getting inside a mirror's reflection while in prison, and eventually developed technology to achieve this goal. Scudder died in Crisis on Infinite Earths and was briefly replaced by Digger Harkness, who eventually went back to being Captain Boomerang.
After Scudder's death, Evan McCulloch, a Scottish mercenary, took on the mantle of Mirror Master. Like his fellow Rogues Captains Boomerang and Cold, McCulloch spent time on the Suicide Squad, though he also battled a cocaine addiction - a situation expressly forbidden by the Rogues.
James Jesse was a circus performer and con-man with a penchant for inventing genius gadgets and then hiding them inside goofy gags. Using his engineering know-how and his twisted sense of humor to vex the Flash, Jesse utilized such magnificent inventions as 'air-walking shoes,' and a variety of circus-themed weaponry as one of Barry Allen's greatest (and most obnoxious) foes.
After Allen's death, Jesse was lured into hell by Neron during the 'Underworld Unleashed' event. Unlike most of his compatriots, however, Jesse was smart enough to recognize Neron as a demon, and used his wits to defeat him. After this Jesse turned coat, deciding to work on the side of the angels.
A second Trickster, Axel Walker, has never gained the prestige of James Jesse, often attempting to join the Rogues, or allying with them only to find himself on the outs due to his psychotic nature and willingness to kill - something the Rogues are usually forbidden to do.
Both Axel Walker and James Jesse have appeared on CW's The Flash with Mark Hamill reprising his role as the older Trickster from CBS's '90s The Flash series.
Nothing says 'comic books!' like a telepathic, super-intelligent gorilla in a purple cape.
Honestly, if you need more than that to understand what makes Grodd such an amazing villain, I don't know what to do for you.
But more than just representing another perfectly executed, yet simple concept for a Flash villain, Grodd has strong ties to Flash's mythos. Hailing from Gorilla City, a hidden society of highly evolved apes with ties to the Speed Force, Grodd has tried time and time again to infiltrate and conquer man's world, butting heads not just with numerous Flashes, but the Justice League, Wonder Woman, and the rest of the cream of DC's super-hero crop.
Although depicting Grodd as he is in comic books might seem like a tall order on a TV budget, CW's The Flash featured a version of the character who gained his mental abilities from a series of experiments.
Several villains have worn the mantle of Zoom - or Professor Zoom (sometimes called Reverse Flash) - over the years.
The original Zoom, Eobard Thawne, proved to be such a menace that Barry Allen was forced to kill him to save his girlfriend's life, leading to Allen's trial for murder.
Later, Hunter Zolomon, an ally of Allen's successor Wally West, with a history not unlike a twisted reflection of Allen's, took up the mantle of the Reverse Flash after a strange explosion caused him to become "unstuck in time."
Eventually, Thawne reappeared, using his time travel abilities to wreak havoc on the also newly-resurrected Barry Allen's past, eventually causing the 'Flashpoint' crisis, which broke reality and leads to the formation of the 'New 52.'
In the 'New 52,' a new Reverse Flash, Daniel West, appeared, though Eobard Thawne later returned.
1. Captain Cold
When it comes to Flash enemies, none of them truly embodies what being a Rogue is all about more than Captain Cold.
A dyed-in-the-wool crook with a heart of gold, Len Snart is one of Flash's oldest foes, and certainly his most persistent. The de facto leader of the Rogues, and their moral center (as twisted as he is) Cold has often shown more cunning than his parka and simple freeze ray would let on, culminating in allying with Lex Luthor and several other villains as an instrumental part of defeating the Crime Syndicate during Forever Evil.
And, despite years spent as a straight-up criminal, it looked for a time like Cold had turned over a new leaf, even briefly joining the Justice League. However, Cold has since returned to a life of villainy as one of the Rogues.
Interestingly, the TV version of Captain Cold also turned over a new leaf, joining a team of heroes on DC's Legends Of Tomorrow - though the character has since been largely retired.