In the 1970s, Batman's comic book started moving away from the camp and childish stories of the 1960s, and The Joker benefited more than most from this. In 1973, writer Denny O'Neil and artist Neal Adams ditched the villain's previous modus operandi of committing exceedingly goofy and mischievous crimes and instead ushered in a version who was a despicable and violent murderer. Physically, he also underwent some major alterations. His normal body structure was given a more gangly and skinny frame, and he just looked a lot more unsettling and strange as a result. The Joker's face was also made gaunt and elongated, making that trademark grin all the more sinister. That might require Jared Leto to adopt some prosthetics, but he has the right build for such a look. Throw in the overcoat and fedora that this era's Joker was often seen in, and this could work perfectly.
