His origin story is that he inhaled Heavy Water vapors and that somehow gave him super speed.
Barry Allen (1956-1986. 2008-current.)
He gained super speed when lightning hit him and he was doused in various chemicals at a laboratory. He then decided to become a super hero and got the name "Flash" from Jay Garrick in a comic book.
Wally West (1986-2011)
Also known as Kid Flash, gained his abilities similar to how Barry Allen got his powers. He also joined the Teen Titans.
Bart Allen (2006-2007)
He is the grandson of Barry Allen and his wife Iris. He started aging very quickly and was kept in a virtual world until in the future, he was brought back in time to find a cure from Wally West.
Powers Of A Flash
As a Flash, the powers of running at super speeds are bestowed upon them:
Super Speed: The two most rememberable Flashes' are Barry Allen and his nephew Wally West. Both of these Flashes' have been recorded to break the sound barrier at 700 Mph, and is even seen rewinding or fast forwarding Time. However, only by 2 or 3 seconds. The Flash or Flashes can also travel the speed of light! While a Flash runs he sees everything in slow motion, and has to take time to look at the beauty of nature by paying attention.
Stamina: As a Flash, their Stamina isn't like most humans or meta humans. They can run for hours and days, without showing any natural tiredness. However, they have to eat a truck load of food to keep their energy up.
Mortal Kombat vs. DC universe
Even though the two universes separated, Flash kept his psychic bond with Liu Kang intact and they would warn each other of any dangers to their worlds. Not long after, Flash comes to Liu Kang's aid to fight off a threat by the sorcerer Quan Chi.
Other Flash Characters
Other Flash characters to have taken up his mantle are:
Unnamed Allen of the 23rd Century
There have also been alternate flashes in different realities:
However within the video game industry it has generally tended to be Wally West who is typically the hero in most games to feature the Flash.