Zoom (also known as the Reverse Flash) is a supervillain from the DC comics and as the name implies is a major antagonist of the Flash and one of the few beings in the DC universe that rivals Flash in speed.
Hunter Zolomon was a survivor of tragedy. His parents had died on the same day, his mother killed by his father, and the police killed his father. He worked for a career in the FBI, but he made a mistake that led to the death of his father-in-law, his wife leaving him, a bad knee, and his discharge from the bureau.
He tried once more to build a life in Keystone City as a profiler with their police department, which made him a target for Gorilla Grodd, who broke his back with a single snap, leaving him paralysed from the waist down. Hunter was driven into the depths of depression by his feelings of helplessness, and insisted the Flash take him back in time to prevent the mistake that cost him everything. The Flash knew first-hand that changing history can easily make things far worst and refused.
Undeterred, Hunter took the F.B.I.'s theories on the workings of the Cosmic Treadmill and attempted to hot-wire the device so that he could use it himself. Instead it exploded, taking the Flash Museum with it, and shifting Hunter onto a faster timeline, effectively giving him super-speed. With his grasp on reality deteriorating, Hunter latched onto a recent discussion about Professor Zoom, and decided he needed to become a new Reverse Flash. He would make the Flash face ultimate tragedy. He would force the hero to understand he must risk everything to prevent it. Zoom was born.
Reverse-Flash appears in The Flash live-action TV series as the tritagonist/main antagonist of Season 1 and a supporting antagonist in Season 2. This version is named Harrison Wells and is the head of S.T.A.R. Labs. He is from a future timeline, since he possesses a holographic newspaper from April 2024 saying that the Flash disappeared in a crisis (a nod to the Crisis on Infinite Earths event where Flash dies). While appearing to be a cripple, Wells can actually walk and rivals Barry Allen in speed, eventually unveiling his facade as Eobard Thawne from the future, Barry's arch-nemesis. Harrison Wells was actually a real scientist who was killed and impersonated by Eobard Thawne and that he's the Reverse Flash. In a tense final stand-off underneath S.T.A.R. Labs, Eddie Thawne, who is Eobard's ancestor, shoots himself, erasing Eobard from existence; however, he re-appeared in the Season 2 episodes "The Reverse-Flash Returns" and "Flash Back" through the use of time-travel.
In Season 2, another foe named Zoom (voiced by Tony Tood, who played Candyman in the Candyman films) appears who serves as the main antagonist. Unlike Hunter Zolomon from the comics, Zoom's appearance shows a black-and-blue version of Barry's suit, along with a demonic mask that appears to be made of skin; in conjunction with the blue lightning that radiates off him, Zoom seems to be based-off Malcolm Thawne/Cobalt Blue or the Black Flash, who serves as the Grim Reaper of speedsters. Zoom comes from Earth-2 and has been causing death and anarchy everywhere he ran, serving as the arch-nemesis of Earth-2's Flash, Jay Garrick. Ever since he discovered the existence of another speedster on Earth-1, he has been sending metahuman criminals to that world to destroy Barry. However, it was later revealed to be an agenda for Barry to get faster so Zoom can steal more speed from him, and gets Harrison "Harry" Wells from Earth-2 to help by holding his daughter Jesse hostage. In the episode "Reverse-Flash Returns", it is revealed that Jay Garrick's Earth-1 counterpart is named Hunter Zolomon, and doesn't have any powers. In the episode "King Shark", shortly after "Escape from Earth-2" in which Zoom manages to kill Jay and pull him back to Earth-2 just before the portal there shut for good, it is revealed that Zoom is identical to Jay, meaning that he is Hunter Zolomon. In "Versus Zoom", it was revealed that "Jay Garrick" was actually the Earth-1 counterpart of Hunter Zolomon/Zoom, who also played the role of the Flash and got a time remnant of himself to assist Team Flash.