Bartholomew Henry "Barry" Allen, also known by his alter ego The Flash, is a fictional character in The CW's Arrowverse franchise, first introduced in the 2013 episode "The Scientist" of the television series Arrow, and later starring in The Flash. The character is based on the DC Comics character of the same name, created by Robert Kanigher and Carmine Infantino and was adapted for television in 2013 by Greg Berlanti, Andrew Kreisberg and Geoff Johns. Grant Gustin portrayed Barry Allen, with Logan Williams and Liam Hughes portraying younger versions.

In the series, Barry is 25 and portrayed as a smart, goofy and tardy character, who works at the Central City Police Department as a forensic chemist. When he was younger, he witnessed the murder of his mother by the Reverse Flash, which resulted in the false imprisonment of his father for the crime. Later in life, while working at the Central City Police Department he is struck by lightning created by the explosion of the S.T.A.R. Labs particle accelerator sending him to a nine-month coma. After waking up he finds himself in S.T.A.R. Labs and develops metahuman powers; the power of speed and he becomes friends with Cisco Ramon and Caitlin Snow. Throughout the series, he constantly trains to become the fastest speedster across the multiverse. Barry uses his powers, along with his team's help, to fight criminals and other metahumans who have misused their powers. He is a friend and frequent ally of Star City-based vigilante archer Green Arrow and Kryptonian superheroine Supergirl.

Gustin appeared as Barry Allen and his superhero persona in crossovers on the television series Arrow, Legends of Tomorrow, Supergirl, Batwoman and the animated web series Vixen, all set within the Arrowverse. The character has also appeared in a digital comic book series. Gustin received critical acclaim for his performance and won an IGN award.

Crime-scene investigator Barry Allen was introduced in the second season of Arrow, in which he arrives in Starling City to personally investigate a superhuman-related crime. He is a fan of the Arrow's exploits and learns Oliver Queen is the vigilante; they become friends. Sometime after Barry returns to Central City, he is struck in his laboratory by lightning which was affected by dark matter from the explosion of S.T.A.R. Labs' particle accelerator.

In The Flash, Barry finds himself with superhuman amount speed, using his powers to fight crime and hunt other metahumans in Central City as a masked superhero known as the Flash of Earth-1 with the assistance of Caitlin Snow, Cisco Ramon and Harrison Wells at S.T.A.R. Labs. When he was a child, his mother Nora Allen was murdered and his father Henry Allen was incorrectly sentenced for the crime. Barry was fostered by detective Joe West, the father of his friend and childhood crush Iris West.

In the first season, Barry awakens from a nine-month coma and eventually identified "Wells" as his mother's murderer as well as the futuristic speedster Eobard Thawne / Reverse-Flash in disguise. Eobard killed Nora after the plan to travel back in time to kill Barry as a child was foiled by the Flash of the future and left stranded in the present day. After capturing Eobard with the assistance of Oliver, Martin Stein and Ronnie Raymond, Barry is given the opportunity to rescue his mother by helping Eobard return to the future. He initially decides to go through with Eobard's offer but Barry decides not to at the last minute as he's warned by his older self not to interfere and instead returns to the present and fights with Eobard, stopping his nemesis from returning to the future. Barry is almost killed but police detective Eddie Thawne sacrifices himself to destroy Eobard.

In the second season, the Flash is recognized as Central City's hero after a singularity event occurs but the event brings the interdimensional speedster Hunter Zolomon / Zoom from a parallel earth who seeks to eliminate all speedsters throughout the multiverse. Barry discovers Eobard's confession of Nora's murder that clears Henry of all charges, and inherited Wells's fortune and resources. Though rich, Barry chooses to continue working for the Central City Police Department while using Wells's money to fund his and his allies's activities with additional assistance from Harry and Jesse Wells. After Zoom kills Henry, Barry defeats Zoom and travels back in time to save his mother's life.

In the third season, Barry alters the timeline by changing the past, resulting in the alternate timeline "Flashpoint". Though he is somewhat able to restore the timeline, this creates new threats, including the god-like speedster Savitar as well as Killer Frost who both have grudges against Barry. When he accidentally travels to the future and sees Iris killed by Savitar, Barry is desperate to change the future to prevent that from happening by working with Vibe, Wally West and Jay Garrick. He learns Savitar is a future version of himself. After saving Iris and defeating Savitar, Barry takes his place in the Speed Force in order to repent for his creation of Flashpoint.