Batman became a very popular character soon after his introduction and gained his own comic book title, Batman, in 1940. As the decades wore on, differing interpretations of the character emerged. The late 1960s Batman television series used a camp aesthetic which continued to be associated with the character for years after the show ended. Various creators worked to return the character to his dark roots, with varying results. The comic books of this dark stage culminated in the acclaimed 1986 miniseries The Dark Knight Returns by Frank Miller, as well as Batman: The Killing Joke by Alan Moore and Arkham Asylum: A Serious House on Serious Earth, among others. The overall success of Warner Bros.' live-action Batman feature films have also helped maintain public interest in the character.
Batman is a founding member of the Justice League of America.
In "The Griffin Equivalency," before going into Raj's office, Leonard suggests to Sheldon that he smile instead of giving comments. Sheldon gives it a practice run, but his first try mimics the Joker, smiling as he plots to kill Batman. The effect is enough to frighten Leonard and Howard.
In "The Hofstadter Isotope," Howard and Sheldon get into an argument over All-Star Batman and Robin the Boy Wonder #8. Sheldon needs it for his Robin Collection & Howard needs it for his Batman collection.
In "The Irish Pub Formulation," Sheldon tells Leonard that he can't keep a secret, even though both Alfred and Batman have their secrets. Sheldon: You know I can't keep a secret! Alfred knows that Barbara Gordon is Batgirl. Which I've now just told to Batman! See, I cannot keep a secret!
In "The Bat Jar Conjecture," Leonard buys Sheldon a Batman cookie jar, before he tells him that he has been kicked off their Physics Bowl Team.
In "The Bad Fish Paradigm," Leonard is trying to get a secret out of a drugged Sheldon. In his stupor, Sheldon claims that the secret is that "I'm Batman."
In "The Speckerman Recurrence," Sheldon tells Leonard that when he faces his high school bully, Batman (i.e. Sheldon) will have his back.
In "The Shiny Trinket Maneuver," Sheldon is seen reading a Batman comic book in the bathroom.
In "The Grasshopper Experiment," Sheldon pulls out his Justice League membership card that is signed by Batman.
In "The Holographic Excitation," Sheldon suggests that he and Amy dress up as Batman and Robin.In "The Celebration Experimentation," Sheldon reveals that he hates his birthday due to his sister and her friends lying to him about Batman coming to their sixth birthday party. To make amends for it, the guys get Adam West to be at the party. Along the way, they all get into a minor argument over who was the best live-action Batman: West himself (pointing out that he had a sense of humor, had his own muscles instead of fake ones, and never had to say "I'm Batman"), Michael Keaton, Christian Bale, George Clooney, or Val Kilmer.