The Flash

The Flash is my brother's favorite superhero in the Justice League. Well, him and the Martian Manhunter. There have been many incarnations of the Flash. His first incarnation is Jay Garrick, and the current incarnations are Barry Allen and Wally West. Every Flash starts out as Kid Flash, training with the Flash as his mentor.
The first Flash, Jay Garrick, is the Golden Age incarnation. He wears a tight-fitting red shirt with a lightning bolt on it and jeans. Garrick also wore a silver helmet with golden wings. Jay Garrick gained his speed by inhaling mineral-saturated water. The Flash's only power is super-speed, unlike Superman's vast array of powers. He was the very first super-fast hero, and among the first single-powered heroes.
The next Flash, Barry Allen, is the Silver Age Flash. He gained his powers when lightning-struck chemicals spilled on him. Barry allen was a forensic scientist. Barry Allen donned the sleek red-and-gold Speedster costume symbolic of the Flash.
The modern incarnations of the Flash are Bart Allen and Wally West. They were both introduced as Kid Flash, wearing a costume similar but not a mirror-image of the Flash's. The Kid Flash costume is more child-like, with a simple eye-mask instead of a mask covering the entire face. Wally West is Barry Allen's nephew through marriage, and Bart Allen's grandson. Both are impulsive, childlike Kid Flashes with a simple-minded view on superheroism.
The Flash is often portrayed as the jester of the Justice League. He is constantly bugging Batman, making mistakes at super-speed. The best thing about the Flash is also something about all superheroes: no matter how differently he acts, he will always do the right thing. He may make many mistakes trying to do the right thing, but he still means to do good. This quality is especially visible in his Justice League television show incarnation. He's usually the guy who gets made fun of, but also attracts ladies. Whiel he may not be the cover-boy of the Justice League, he is one of the most well-known. The Flash of the Justice League refers to the Speedster, not the old, Gold Age Flash of the Justice Society.
The Flash is a pretty funny guy. He draws younger audiences to the Justice League and the DC Universe because he's funny and he makes mistakes. The other superheroes seem like they never do anything wrong, especially Batman. Flash kind of blunders his way through the comic or cartoon or story, but is still seen as the hero in the end. He's also not the smartest member of the Justice League. Many people probably pay attention to the League just to see him get made fun of by villains or other members. He is much like Marvel's Spider-Man: people can (kind of) relate to him.