In the comics, the Flash is a mantle used by four superheroes who protect the cities of Central and Keystone City. The Flash is hailed as "the fastest man alive", faster than Superman, derived from the extradimensional "Speed Force", from a which a variety of speed-applied powers originate. When asked about which incarnation of the Flash would be appearing in The Batman, Alan Burnett said that he sees Flash as Barry Allen, though they're leaving it up to the viewer. He is voiced by Charlie Schlatter, who voiced a Flash from Superman: The Animated Series, though the Flash on S:TAS is later revealed in the series spin-off JLU to be Wally West.

Flash is a fast, get things done kinda guy, though he also has quite the sense of humor and likes to be a loner at times. He also likes to talk fast.

Info from Wikipedia and Self