Ledger's method acting in The Dark Knight resulted in a breathtaking performance, although it seemed to have taken a toll on his mental health. In his new book Don't Look Back, You'll Trip Over: My Guide to Life (via People ), Caine spoke about his relationship with the late actor. He mentioned his temperament, offering:

Everyone knows that of all the different takes we’ve seen on the superhero genre over the years, it was Heath Ledger ’s Joker that has gone down as one of, if not the absolute, best performances of all time.