"Robin War" is a comic book crossover storyline published by DC Comics.
 The event ran from December 2015 to January 2016 in the books "Robin War", "Grayson", "Detective Comics", "We Are Robin", "Robin, Son of Batman", "Gotham Academy", "Red Hood/Arsenal", and "Teen Titans".
Batman: The Killing Joke is a 1988 DC Comics one-shot graphic novel featuring the characters Batman and the Joker written by Alan Moore and illustrated by Brian Bolland.
 "The Killing Joke" provides an origin story for the supervillain the Joker, loosely adapted from the 1951 story arc "The Man Behind the Red Hood!
".
 Taking place over two timelines, "The Killing Joke" depicts the Joker attempting to drive Jim Gordon insane and Batman's desperate attempt to stop him.
The Red Hood is an alias used by multiple fictional characters and a criminal organization appearing in American comic books published by DC Comics.
 Jason Todd is the most widely known version of the incarnation, and he assumes the Red Hood identity in the main DC Comics continuity.
Red Hood and the Outlaws is a superhero comic book published by DC Comics.
 Commissioned in response to the growing popularity of the character of Jason Todd, a former protege of Batman who took a turn as a villain following his resurrection, the book depicts Jason's continued adventures as the Red Hood, on a quest to seek redemption for his past crimes, forming a small team with two of his fellow anti-heroes.
"Batman: Under the Hood" (also known as "Batman: Under the Red Hood") is a comic book story arc published by DC Comics, written by Judd Winick and primarily illustrated by Doug Mahnke.
 Featuring Batman in the monthly title of the same name, it ran from November 2004 to June 2005, before going on a short hiatus and returning from November 2005 to March 2006.
"The Man Behind The Red Hood!"
 is a comic book story arc in the "Batman" and "Detective Comics" series.
 It features Batman and a few University students trying to crack a decade-old case.
 It features the earliest origin story for the Joker.
"Death of the Family" is a 23-issue comic book story arc first published by DC Comics in 2012 featuring the fictional superhero Batman and his family of supporting characters.
 The arc spans several titles featuring characters of the Batman family including: "Batman", "Batgirl", "Batman and Robin", "Catwoman", "Detective Comics", "Nightwing", "Red Hood and the Outlaws", "Suicide Squad", and "Teen Titans".
 The story involves the return of Batman's arch-enemy, the Joker, and his plan to destroy all of the people Batman has come to rely on over the years: the multiple Robins, Batgirl, Catwoman, Alfred Pennyworth, and Commissioner James Gordon.
 The title is a reference to the classic Batman story arc "" (1988), in which the Joker murders Jason Todd.
The Joker is a fictional supervillain created by Bill Finger, Bob Kane, and Jerry Robinson who first appeared in the debut issue of the comic book "Batman" (April 25, 1940), published by DC Comics.
 Credit for the Joker's creation is disputed; Kane and Robinson claimed responsibility for the Joker's design, while acknowledging Finger's writing contribution.
 Although the Joker was planned to be killed off during his initial appearance, he was spared by editorial intervention, allowing the character to endure as the archenemy of the superhero Batman.
"Batman and Son" is a 2006 comic book story arc featuring the DC Comics character Batman.
 Written by Grant Morrison and drawn by Andy Kubert, the story was published in four parts in the comic book "Batman" starting in #655 and ending in #658.
 The story was the beginning of Morrison's run in the "Batman" comic as well as his long-term take on the character of Batman through multiple titles over the next seven years.
 The arc introduced Batman's son, Damian Wayne, bringing him into the mainstream continuity of the DC Universe.
Batman: Under the Red Hood is a 2010 American animated superhero direct-to-video film produced by Warner Bros.
 Animation and released by Warner Home Video.
 It is the eighth feature in the DC Universe Animated Original Movies series.
 It was released on July 27, 2010.
 The film stars Bruce Greenwood as Bruce Wayne/Batman, Jensen Ackles as the Red Hood/Jason Todd, John DiMaggio as the Joker, Neil Patrick Harris as Nightwing/Dick Grayson, Jason Isaacs as Ra's al Ghul, and Wade Williams as Black Mask.
 The screenplay was written by Judd Winick, who also wrote the "" run in the monthly "Batman" comic.As in the comic, it focuses on Batman dealing with the return of his former apprentice, the second Robin, Jason Todd , who now goes by the moniker of Red Hood, a murderous vigilante and the former alias of Batman's archenemy , The Joker , on whom Jason is trying to exact revenge.

Question: When did the supervillain portrayed by John DiMaggio is Batman: Under the Red Hood first appear in the comic book "Batman"?
Answer: April 25, 1940