“A final interpretation of the Joker’s [conflicting ‘how I got these scars’] stories is that the Joker is making a powerful comment on the DIFFERENCE between Joker and Batman.
“If we look at Batman, his origin story is central. It is not just an explanation for his powers, like Peter Parker’s radioactive spider or Superman’s planet Krypton. Batman’s origin story is his MOTIVATION for becoming Batman. Batman is not the result of a scientific experiment gone wrong, like the Hulk; Bruce Wayne made a conscious CHOICE to become Batman after his parents died. Batman’s origin story is also the source of a painful tension in Bruce’s character: his conflicting desires for revenge (violence and vigilantism) versus justice (law and order). In short: Batman is defined by Bruce Wayne’s past. … By telling conflicting stories of his origin, Joker draws a powerful contrast with Batman. Batman is defined (and limited) by his past.
“The Joker is free to invent his own past. Since he has no past, he has no motivation. … In short, Joker is defined by his LACK OF a past.
“Batman is scarred (psychologically) by his parents’ death and he never forgets it. The Joker doesn’t even bother to remember why he has scars. The Joker uses people’s pasts to manipulate them several times in THE DARK KNIGHT. At the most superficial level, Anna Ramirez is corrupted thanks to her mother’s hospital bills.
“Going a little deeper, the Joker corrupts Harvey Dent by appealing to his lifelong appreciation for fairness (represented by the coin). The person who has the most vulnerable past is Batman himself. The Joker is able to get the better of Batman several times because of this. First, the Joker forces Batman to crash his bike rather than violate his one rule. ”
Then, the Joker is immune to Batman’s beatings and intimidation because he knows Batman can’t kill him. Ultimately, Joker tricks Batman into letting Rachel die by sneakily appealing to his secret love for her. The Joker is a man without a past, and that’s what makes him a terrifying villain.”