I sat around in a hotel room in London for about a month, locked myself away, formed a little diary and experimented with voices — it was important to try to find a somewhat iconic voice and laugh. I ended up landing more in the realm of a psychopath — someone with very little to no conscience towards his acts … just an absolute sociopath, a cold-blooded, mass-murdering clown.... [being given] free rein [by director Christopher Nolan was] fun, because there are no real boundaries to what The Joker would say or do. Nothing intimidates him, and everything is a big joke.
Interview remarks published in Empire, from interviews conducted in November 2007.