Joe Chill is the man responsible for Bruce Wayne turrning into Batman.
Joe Chill was Man-Bat's assistant when he (Man-Bat) was a human.
When he went to ace chemicals, a chemical that fell into his eyes can let him resist the next thing that goes into his eyes.
Acid fell into his eyes. He killed Bruce Wayne's parents wih this new power.
He was a helper of Man-Bat known as Acidman.