As far as I know there are 4 characters who have taken the mantle of The Flash: Jay Garrick, Barry Allen, Wally West and Bart Allen. Why are there so many versions? Do they have any differences in power? And if so, what are they?
There were four primary Flashes of the DC Universe. Since the New 52, DCnU, we have only seen two, Barry Allen has returned to wearing the mantle of the Flash and Bart Allen was resurrected and is now functioning in the role of Kid Flash.
In the DCU (the previous continuity of the DC Universe)
The Golden Age Flash: The Flash of Earth-2 was also Jay Garrick, the original speedster of the DC Universe, who gained his powers via radiation accident breathing in radioactive fumes from "hard water". He was known for his distinctive red and blue uniform and silver winged hat. He was a regular member of the Justice Society of America.
Kid Flash, later Flash: Wally West was the nephew of Barry Allen and gained his powers in a laboratory accident similar to his uncle, Barry Allen. He became Barry's sidekick and debuted as Kid Flash. Kid Flash was a founding member of the Teen Titans and was a regular member of that team until he took up the mantle of the Flash.
After Barry Allen's death in the Crisis on Infinite Earths, Wally West experienced anxiety and his powers were temporarily reduced. Wally eventually develops his powers and becomes the most powerful Flash known, utilizing the Speed Force in ways Barry never did. He had a very long run as Flash and most people remember him in the Flash of the Justice League Animated Series - JLA and JLU.
The Flash: Barry Allen was the Silver Age analog of the Flash, who lived on Earth-1. Barry Allen has been returned to the mantle of the Flash in the DCnU. Barry was one of of the founding members of the Justice League of America and one of its most popular members. He had a long term friendship with Hal Jordan and the two often teamed up successfully. Barry's exploits had become legend in the DCU and his death was often lamented as the price of the Crisis on Infinite Earth saga. His revival was met with some consternation as Wally West had grown into the role very well and with the reboot if the DCnU, Wally has not been seen yet.
Flash of Earth 2 - Jay Garrick, Kid Flash - Bart Allen, The Flash - Barry Allen
Like so many things in the DC Universe, Barry Allen has been reset to reprise his role of prominence as the Flash, and Wally West is nowhere to be seen. Barry has begun utilizing his powers in new and different ways from previous incarnations of the character.
In the DCnU, there has been no sign of Jay Garrick on Prime Earth, though promotional images of him have been seen in a revamped costume. The revamped version of Jay Garrick has debuted in the new series Earth 2, a parallel Earth (one of the parallel worlds which comprise the new DCnU, there are 51 other Earths). Hints of Wally West resurfacing in the DCnU have begun to be bandied around the internet.
One slight difference in powers was that Barry was able to vibrate his molecules and pass through solid objects. Wally could vibrate his molecules, but would make things explode if he passed through them. Also, Wally was able to lend and borrow speed from objects, which Barry never did.
Wally could make things explode, but after learning about the speed force, he was able to control this and vibrate through things without needing to. Additionally, Wally's ability to manipulate the speed force allowed him to do a lot of things Barry couldn't, most notably:
- He could run through time without the need for the cosmic treadmill (Flash #0 from Zero Hour).
- He could give/take speed from others (numerous).