The Flash is the name of several superheroes appearing in comic books published by DC Comics known for their "super speed", which includes the ability to run, move, and think extremely fast, and possess superhuman reflexes.
In "A Hero Sits Next Door", he watches Peter play strip poker with Wonder Woman alongside the rest of the Justice League.
In "The Woof of Wall Street", Stewie complains that Brian's greed has ruined a good team like Ricki and the Flash and confuses the superhero known as 'The Flash' for the Meryl Streep film. Brian and Stewie deny having seen the film at first, but both admit to having seen it after all.
In "Send in Stewie, Please", Stewie says that he and Grant Gustin would make the perfect Facebook couple, and tells Dr. Cecil Pritchfield that he is the actor who portrays the The Flash on the CW show of the same name.