Main Flashes:
* Jay Garrick (Golden Age Flash): The original Flash, he gained his powers from a vat of chemicals and was a major hero during World War II.
* Barry Allen (Silver Age Flash): The most iconic Flash, his powers were granted by lightning and he was a key member of the Justice League.
* Wally West (Third Flash): Barry Allen's sidekick Kid Flash, he inherited the mantle after Barry's death and continued the legacy.
* Bart Allen (Fourth Flash): Barry Allen's grandson, he was super-fast from birth due to his connection to the Speed Force.
Other Flashes:
* Jesse Quick (Impulse/Jesse Chambers): Daughter of Johnny Quick, she also possesses super speed.
* Max Mercury: A speedster with a connection to the Speed Force.
* Daniel West (Reverse-Flash): A villain with super-speed, a rival and enemy of Barry Allen.
Therefore, it's impossible to say exactly "how many" have been The Flash, as it depends on how you define it. But there have been several individuals who have donned the mantle and used the name "The Flash" throughout the decades.