One of Gotham's most hated criminal bosses, there aren't many villains
The Joker might admire however, DC has proven that he is a fan of at the very least: The Riddler.
Joker as well as Riddler are frequently enemies that are a part of Batman
that have been caught in each others' hairs in the same way as The Batman's.
Although they are often on the opposite side, the two have clashed on a number of occasions.
The two criminals formed the alliance to fight The Caped Crusader throughout his second year as a police officer