Batman has had to contend with many villains and supervillains since he first appeared in comic books in 1940, and arguably, the Joker is his greatest nemesis; the Joker appears as the villain in the very first Batman comic book, and he has steadily remained a factor in Batman's crime-fighting activities through the different interpretations and iterations of the Batman story. However, though the Joker is arguably the primary villain that Batman has had to deal with over time, he is far from the only major villain character in the Batman canon. Other villains, such as Catwoman, Two-Face, Poison Ivy, Bane, Ra's Al Gul, the Penguin and Harley Quinn are also closely associated with Batman both in comic books and in television, video game and film adaptations of the Batman narrative.
Because the Joker is one of the oldest and most iconic Batman villains, it is easy to argue that he is Batman's greatest enemy. However, other villains, such as Ra's Al Gul, seem to present more of a challenge for Batman than the Joker does, or at least present a different type of evil than the Joker represents. The Joker is undeniably dangerous, but Ra's Al Gul is focused on more than just antagonizing Batman and doing harm within Gotham.