Flashpoint - Batman: Knight of Vengeance. "This is an alternate universe where Bruce Wayne died instead of his parents. Causing His father Thomas Wayne to become Batman and his mother Martha to go insane and become the Joker.
This is an infographic made by Mashable showing the most popular superheroes and villains as determined by social media mentions. It should come as no surprise that Batman and the Joker got number one, because they're my personal favorites.