- "Chasing down time criminals and fixing the parts of history they screwed up. Aberrations, the captain called them."
- —Mick Rory[src]
Aberrations, also known as temporal aberrations or historical aberrations, are massive alterations of the existing timeline. They are generally prompted by the efforts of time criminals, disrupting the flow of time with anachronistic weaponry, meta-human abilities and other factors that could change the course of events, which slowly cements and affects a timeline's future. According to Rip Hunter, it would take some time for the consequences of an aberration to ripple throughout time; those safe inside a temporal zone would remain unaffected by the changes. 
Unusually large aberrations would also generate time quakes, emitting shockwaves in the temporal zone. An aberration could happen due to a time pirate selling futuristic weaponry to denizens of the past, or a "time criminal" willfully disrupting the timeline for one reason or another. 
A historical aberration would not immediately substitute the reality of the future, allowing the protectors of timeline some leeway and additional attempts in preventing the aberration's effects. The aberrations were prompted by rogue time travelers, such as a time pirate or a "time nemesis", as the Waveriders crew unknowingly described the Reverse-Flash. Some of the denizens of the future would notice the effects of an aberration, recognizing that the reality is not as it's supposed to be. 
After the fall of the Time Masters, Rip Hunter's team, calling themselves "the Legends", decided to take it upon themselves to protect the timeline from devastation, locating temporal aberrations through Gideon and going on missions to ensure the events pass more or less as they originally did, minimizing the aberrations' effects on the timeline. The Legends tackled on a number of such aberrations, one of which was the appearance of blaster-wielding assassins in 17th century France, seeking to kill the royal family. 
After the French aberration case, Rip Hunter and Gideon calculated a 96% likelihood of another aberration in Bhopal, 1912. However, before they could attend to it, the Waverider was shaken by a time quake, originating from a cataclysmic aberration in New York City, 1942. The aberration would have long-going consequences, such as an atomic bomb drop on New York, a prolonged World War II until the year 1947, with many more casualties, and historical sources telling of such a war appearing all the way to the future of 2016, while the denizens of 2016 would still recount historical events as they were originally learned, with some of them, like Nate Heywood noticing that something wrong is happening with reality itself. 
The 1942 aberration, while going according to Adolf Hitler's plan, was fueled by the efforts of the near-immortal Damien Darhk and, on some level, his time-traveling meta-human partner Eobard Thawne. Darhk would provide the Nazi regime with uranium, while their plans also required the abduction of Albert Einstein and Mileva Maric, the only people capable of creating the atomic bomb by 1942. After their two time-travel attempts, the Legends both forced Darhk into wasting his nuclear missile on the Waverider, instead of the original target, New York City, and prompted Albert Einstein to reveal his ex-wife's role in scientific research to the public, making the United States government to provide security from the Germans to both Einsteins, safeguarding them. Realizing the plan's failure, Darhk and Thawne double-crossed the Nazis, as the Reverse-Flash slaughtered the U-boat's crew before greeting his partner. On their side, the Legends mused on the possibility of a rogue time traveler, a "time nemesis", helping Damien Darhk and the Nazis blow up New York City for their own amusement. 
Although the aberration's effects were prevented in New York City, it continued in 1942 due to Eobard Thawne's biomolecular enhancer ending up in the hands of Baron Krieger. With the enhancer allowing Krieger to transform into a meta-human form, the lives of the Justice Society of America members were in grave danger, forcing the Legends to return back to 1942 from the Temporal zone and stop Krieger. Their mission was successful, with the biomolecular enhancer ending in Ray Palmer's hands, but the Reverse-Flash ended up taking the Askaran Amulet and killing off Rex Tyler, partially erasing his timeline. 
Another aberration happened back in the 19th century, the times of the Civil War in the United States. A time pirate ended up crashing with TX-90 virus onboard his timeship, causing an outbreak of the disease that turned people into a state akin to that of "zombies" from classic horror movies. The outbreak threatened to affect the course of the Civil War, allowing the Confederates to lead the Union army into a trap, ultimately winning their independence from the United States. The Legends were fast enough to destroy the source of virus before it was too late, but the "zombified" Confederacy soldiers still ended up sacking Collins Plantation and attacking Ulysses S. Grant's forces of the United States Army, before being blown up by the efforts of Steel, ending the aberration's effects. 
Eobard Thawne and Damien Darhk continued to be the source of aberrations, having H.I.V.E. members, including Darhk himself, infiltrate the White House, and somehow causing infinitesimal ripples in time that affected Martin Stein's movements. Darhk and Thawne acquired another artifact from the Soviet Union's KGB, although the plan to blow up the White House, along with Ronald Reagan and Mikhail Gorbachev was all for naught. The Legends' own involvement caused a massive panic, with the sightings of the "rocket man" (Firestorm) dominating the headlines of Channel 52. Sara Lance ended up revealing Damien Darhk his ultimate fate from the timeline as she knew it, forcing him into a state of despair. Thawne suggested to save Darhk and alter his destiny, granting his partner a Time Sphere and time traveling together.
Nevertheless, Darhk and Thawne's machinations proved to be not the only cause of aberrations, when the Legends came to deal with another mishap on behalf of a time pirate, who was seeking the dwarf alloy source in 1874, only to get killed by Quentin Turnbull after revealing the location of dwarf alloy to him. Turnbull's obtaining of dwarf alloy would lead to an aberration resulting in the creation of "Turnbull Country" carved out of the USA's west coast by 1876. Assisting Jonah Hex, the Legends succeeded in apprehending Turnbull and preventing the aberration timeline, with Nate Heywood stopping the train loaded with explosives that could potentially cut off the United States Army from reaching the country's western territories.
While dealing with the crisis of Dominators in 2016, Martin Stein realized that, to his horror, the advice he has given to his younger self regarding Clarissa resulted in an aberration in human form: an appearance of Lily Stein, a daughter he never had, with memories of her and their life together painfully coming together to Professor Stein's head. Although he contemplated going back in time to erase his "mistake", Stein changed his mind after words of advice from Caitlin Snow and Jefferson Jackson, deciding to protect his daughter and keep her existence a secret from the rest of the Legends.
Professor Stein's secret came into light during the next aberration crisis caused by Eobard Thawne's syndicate, this one concerning a murder of Eliot Ness in 1927 resulting in Al Capone's rise to the Mayor's Office of Chicago, introducing Oktoberfest. While correcting the aberration, Stein has gotten memories of his whole life with Lily, and revealed them to Sara Lance. Although, initially the new leader of the Legends thought that Martin should correct this "false" reality, later on, she agreed that, ultimately, happiness and family may be worth more than the sanctity of one version of history. Which, considering the Legends' killing of Tokugawa Iemitsu, should have been clear for them a long time ago.
Continuing their hunt for the Spear of Destiny, the Legion of Doom set up another aberration to get the Legends' attention while they would hunt for the missing pieces of the spear. Aside from killing Cal DeVito, who was supposed to create a new carburetor for shovelhead motorcycles, they also attacked the filming set of Rip Hunter and George Lucas, causing the latter to decide to abandon his career as a director. The resulting anomaly robbed Ray Palmer and Nate Heywood of their powers and abilities, as the two never got interested in sciences without watching Lucas's films. The Legends managed to undo the second aberration, if not the first, but at the cost of Rip Hunter being taken prisoner.
The Legion of Doom managed to "reprogram" Rip, binding him to their will, and sending him on a successful mission to bait the Legends with an aberration while taking a piece of the Spear. The Aberration in particular being the assassination of George Washington by Rip, and the arming of the soldiers of England with advanced modern weaponry to use against the Patriots. The Legends arrived in time prior to the assassination, which Rip anticipated (despite already seemingly succeeding in killing Washington once) and ambushed them with his English troops, along with the leaders of the Patriots. While most of the Legends dealt with the crisis regarding the American Revolution, Rip himself boarded the Waverider, almost killed Sara Lance and forced Jefferson Jackson to give him the piece of the Spear of Destiny.
Another aberration was related with to the actions of heroes rather than villains: after the Justice Society of America's last mission, Stargirl was among the heroes time-scattered by Rip Hunter to guard the pieces of the Spear, never allowing its reality-warping powers to be in one person's hands. Ending up in the year 507, she settled in the middling British kingdom of Camelot and decided to turn it into the Camelot reminiscent of Arthurian legends, taking on the role of Merlin the Wizard and using advanced sorcery and tech to guide the kingdom to a level of society, culture and technology more akin to the High/Late Medieval period than the Dark Ages it was supposed to be in after the collapse of the Roman Empire. Nate Heywood noted that both the court of Camelot and his teammates ended up dressed more like something befitting a Renaissance party than the clothes of Medieval's Dark Ages.
DC's Legends of Tomorrow
- "Who Are You?" (mentioned)
Behind the scenes
- In DC Comics, Aberration appears as an entity with reality-altering powers, rather than as a reality-altering event.
- Although the Legends didn't seem to notice, their own killing of Tokugawa Iemitsu ten years before his actual death in history would also radically alter the timeline, as the Tokugawa dynasty continued from Iemitsu's second son, who wasn't born yet in 1641. It's unknown why the team disregarded that, or how they did they fix the aberration, if they even tried to.
- The general existence of Lily Stein is considered an aberration unlike John Diggle, Jr. who replaced Sara Diggle (his counterpart from a pre-existing timeline), as the Steins were a childless couple during the original timeline.
- For unknown reasons, the Legends were not made aware at first that Barry Allen changed the timeline and created Flashpoint. Even more so, The Legends have not considered the changes afterwards (Dante Ramon's death, Caitlin's new powers, and Sara Diggle being erased from the timeline) as being considered aberrations that needed to be fixed.