After much research, Nolan's brother and co-writer, Jonathan Nolan, suggested the Joker's first two appearances, published in the first issue of Batman (1940), as the crucial influences.
Logo de moita investigación, o irmán de Nolan e guionista Jonathan Nolan suxeriu que as dúas primeiras aparicións do Joker, publicadas no primeiro tomo de Batman (1940), como as principais influencias.