there is not only batman...to day if batman is batman that goes to thouse villains for whome this charecter is created...joker gives him a reason to create himself. if there is negetive point then a positive will attracted towords negtive point..and they stay together...Christopher Nolan mostly focus on negetive more than a positive one in his dark knight series...and he established relationship between a villain and hero...if there is no Joker..then there is no need for batman...