Meta-humans

Meta-humans, often shortened as metas, are individuals who acquired superhuman abilities after experiencing mutation of their bodies (in comparison to magic users, who learned how to harness primordial energies without being mutated themselves). Most obtained their powers after surviving an explosion caused by a malfunction of the S.T.A.R. Labs particle accelerator on December 11, 2013. They were exposed to the particles and dark matter that altered their genetic, chemical, or even atomic structure, giving them a variety of abilities. These abilities seem to often relate to what energy or matter they were directly in contact with at the time of exposure.

On Earth Two, intending to prevent the negative effects of the particle accelerator, Dr. Harrison Wells of that universe allowed excess radiation to flow underground, with the first meta-human appearing 11 hours following.

Overview
Meta-humans are represented by a wide spectrum of mutated people, with mental state, physical appearance and physiological specifics unique for each individual. The conditions they were in during the exposure to the mutative element seem to affect how the mutation changes a person. Furthermore, there are dormant meta-humans, like Henry Hewitt and Jefferson Jackson, whose powers did not resurface until the connection to Firestorm Matrix, which either re-enabled their mutative physiology, or represented a new mutation altogether.

Most meta-humans seen on Earth One and Earth Two mutated after exposure to dark matter connected to the S.T.A.R. Labs particle accelerator. Some meta-humans acquired their powers through other means, not directly related to being hit by the wave of dark energy after the particle accelerator explosion. Among such meta-humans are Eliza Harmon (used Velocity serums to give herself superhuman speed, although she may have been a dormant meta-human prior to that), Valentina Vostok (used the Operation Svarog version of Firestorm Matrix to become a Soviet Firestorm) and Jake Simmons (source of mutation unknown). Additionally, while originally thought a product of magic, it was eventually revealed that the immortality and regeneration of Vandal Savage, as wells as reincarnation and bird-like powers of Hawkman and Hawkgirl are the result of mutation due to exposure to advanced futuristic technology stored in the "meteor" from Thanagar.

It is arguable whether those affected by the Mirakuru drug can be considered true meta-humans. On the one hand, their case is similar to that of Eliza Harmon, who amplified herself with the Velocity drug, receiving meta-human powers at the cost of negative effects for sanity. On the other hand, their condition is reversible, as a Mirakuru cure was created, that allowed to cure Slade Wilson and Roy Harper. However, the Flash's meta-human powers were also taken away from him when Hunter Zolomon stole his speed, turning him into a normal human once again. Additionally, Slade Wilson was affected by the Mirakuru for years, implying that he would retain his superhuman abilities if not for the cure. One way or another, Barry Allen researched the case of Cyrus Gold, a Mirakuru-affected member of the Church of Blood as part of his hunt for "the impossible", which otherwise included meta-humans.

Some meta-humans consider themselves separate, or at least different enough from the regular humans to identify as something else. The prime example of such thinking would be members of Zoom's meta-human group, who ushered in the Metapocalypse upon Central City. In the speech before his followers, Zoom depicted humans as the archetypal "Other", claiming that they think that Earth One belongs just to them, and inciting the meta-humans under his command to take over this world. Characteristically of this group, Killer Frost, Black Siren, King Shark and Reverb were all shown preferring to refer to themselves with their meta-human "names", instead of their original ones. Interestingly, Hunter Zolomon himself preferred to be called by the name of the man whose identity he stole, Jay Garrick, rather than his own meta-human nickname, or especially his real name, as shown when Caitlin Snow called him "Hunter", causing Zolomon to relieve a painful traumatic flashback.

Meta-humans are not to be confused with magic users, like Damien Darhk or John Constantine, who receive their powers not thanks to mutation, but by manipulating primordial energies of the universe, such as Light of the Soul. However, it is possible for an individual to exhibit both magic powers and abilities related to mutated physiology, Vandal Savage being a prime example of such.

History
Due to the time travel adventures of Rip Hunter's team, meta-humans such as Firestorm have been sighted in different points of time. After witnessing Firestorm, Vandal Savage started an extensive study of meta-humans. On the one hand, his research proved fruitful when another meteor from Thanagar landed in Harmony Falls, allowing Savage to create imperfect Manhawks using mutative Thanagarian technology. On the other hand, Savage assisted the Soviet Union with research of his own, culminating in Operation Svarog, which would produce a Soviet Firestorm.

Nevertheless, the meta-humans remained a mystery to the world at large, and superhuman powers were generally considered impossible. The trend would continue until 2020, when the S.T.A.R. Labs particle accelerator, created by Tess Morgan and Harrison Wells, exploded, giving birth to many meta-humans such as the Flash. However, these events were ultimately rewritten in the year 2000, when a yellow-clad time-traveling meta-human Eobard Thawne changed history, first by slaying Nora Allen, the mother of Barry Allen, the future Flash, and then by being stranded in time and having to take on Harrison Wells's identity, to ensure that the particle accelerator explodes and Barry becomes the Flash. As the result of Eobard's knowledge from the future, S.T.A.R. Labs was able to create a working particle accelerator much earlier than in the original timeline, resulting in a massive influx of meta-humans in the years 2013-2014.

Barry Allen, who witnessed "the Man in Yellow", was sure that he was the one who killed Barry's mother, and Henry Allen was innocent. Seeing his mother killed by "something impossible" motivated Barry to give special attention to cases connected to the meta-humans, which would appear paranormal to the general population, trying to prove that "the impossible" was real. After becoming an assistant CSI in Central City Police Department, Barry started searching for super-powered beings in the hope that he will prove one case true and subsequently, find answers to clear his father for his mother's murder. Among such cases was the rampage of Cyrus Gold, a man mutated due to the Mirakuru drug, giving him superhuman strength, endurance and vitality. Mirakuru was also harmful for one's mental state, turning its users into killing machines, something that was also characteristic of the meta-humans post-explosion of the particle accelerator.

In the year 2013, S.T.A.R. Labs particle accelerator exploded, covering Central City and its outskirts with a wave of dark matter energy, exposing countless people to physiological mutations. Hartley Rathaway, one of the victims of dark matter exposure, suspected that Dr. Harrison Wells knew of the high probability of the explosion, and still risked with lives of many people. However, with Dr. Wells actually being Eobard Thawne, a meta-human from the future, the explosion was his goal all along. "Wells" assembled a team with his loyal employees Caitlin Snow and Cisco Ramon and asked Joe West, Barry Allen's adoptive father, to be allowed to care for the comatose Barry in S.T.A.R. Labs, intending on making sure that Allen becomes the Flash.

Barry eventually started to work with "Wells" and the other scientists of S.T.A.R. Labs, organizing themselves as Team Flash, with their goals turned to fighting crime in the Central City area, specifically, with apprehending meta-human criminals, which were sent to the Pipeline, or, later, to the Iron Heights Prison. Some meta-humans were recruited by Leonard Snart, who broke them from captivity along with Lisa Snart. Eventually, other members of Team Flash discovered Dr. Wells's true identity as the Reverse-Flash, the man who killed Nora Allen, and managed to defeat him with the help of the Arrow and Firestorm.

After the confrontation with Eobard Thawne and the resulting appearance of the singularity above Central City, the Flash and Firestorm saved the day at the cost of Ronnie Raymond's life. Their victory darkened by the loss and the betrayal, Team Flash members temporarily went their separate ways, before having to re-unite due to the appearance of "breacher" meta-humans from Earth Two, led by Zoom. Team Flash, joined by such denizens of Earth Two as Dr. Harrison "Harry" Wells, Jesse Quick and Jay Garrick, opposed Zoom's meta-humans, culminating with Jay's apparent death. In truth, "Jay" manipulated the events all along, being the mastermind behind Zoom's invasion. Declaring Earth Two to be already under its knees before his power, Zoom led the meta-humans of his home universe to Earth One, capturing the CCPD station and declaring that this Earth belongs to meta-humans. Zoom's invasion, nicknamed "the Metapocalypse" by the people of Central City, was ultimately stopped thanks to the joined efforts of CCPD and Team Flash, with many meta-humans incarcerated in the meta-human wing of the Iron Heights.

Among the meta-humans Barry Allen encountered were specific individuals that mutated without direct relation to the particle accelerator explosion. The real Jay Garrick, for example, exhibited similar speedster powers as Barry himself, but the source of his powers is unknown. Some meta-humans stayed dormant for a while, before their hidden powers being awakened by specific events, like memories of a changed timeline (Vibe experienced his meta-human powers after Barry aborted a timeline in which Central City was destroyed by a tidal wave and Cisco was slain by Eobard Thawne), or Firestorm Matrix exposure (Henry Hewitt and Jefferson Jackson were both diagnosed as being mutated just enough to allow for a merge with Martin Stein in form of Firestorm, and although the former was unsuccessful, the experiment awoke his own powers as "Tokamak"). However, Barry Allen recognized that Vandal Savage's fighting abilities were not meta-human in nature, but a result of magic, same as Kendra Saunders, initially thought by Cisco Ramon to be a meta-human.

However, while Savage was indeed a magic user and wasn't affected by the particle accelerator explosion, he later found out and revealed to Kendra that his powers of immortality and regeneration, as well as Hawkman and Hawkgirl's bird-like powers and reincarnation, were not actually magic, but a result of physiological mutation due to the exposure to Thanagarian technology, advanced beyond that of humanity's, and stored in what appeared to be meteors. Savage intended to use this technology to wipe out the timeline and reverse it back to the times of Ancient Egypt, allowing himself to rise as Hath-Set, the ruler, not just a secret advisor or manipulator. However, he was ultimately slain by Kendra Saunders and Scythian Torvil in the year 2021, his plans foiled.

Powers and abilities
There is a wide range of meta-human powers, including everything from time distortion to elemental manipulation. Meta-humans who gained their abilities from the dark matter explosion in Central City often have powers influenced by unusual conditions at the time of exposure: Barry Allen was struck by lightning and gained access to the Speed Force, giving off electricity when he runs at superhuman speeds, while Tony Woodward and Joseph Monteleone gained the power to transform into the substance they were immersed in during the explosion (steel and tar, respectively).

Due to their altered physiology certain meta-human powers affect meta-humans differently than normal humans. Barry remained infected by Roy Bivolo's powers for some time while their effects only lasted 5 minutes for a normal person.

The emotional state of a meta-human also has an influence on their powers; reacting and strengthening when the meta-human is in a state of emotional stress.

Behind the scenes

 * In DC Comics "Metahumans" are a loose term to describe any and all beings with superpowers. Although stricter classification exists in-universe (with Homo Maji, magic users, being a separate group from the weilders of "Metagene"), different types of superhumans are often lumped together, while "Arrowverse" continuity clearly distinguishes mutated humans from other superpowered beings.
 * The term "meta-human" usually refers to a mutated human, hence the suffix. However, Grodd is a mutated non-human that still displays powers that would allow to classify him as a meta-human. The meta spiders are a similar case.
 * While Wally West and Jesse Quick did not show signs of having meta-human powers after getting hit by a wave of dark matter, they may be dormant meta-humans whose powers have not resurfaced yet, similar to Henry Hewitt and Jefferson Jackson before the two were introduced to Firestorm Matrix. A sign of possible meta-human powers may be the lightning-like Speed Force energy that went from Barry's hand to Jesse's. Additionally, Wally ended up mutating and becoming the Flash/"Kid Flash" in the Flashpoint timeline.