The Joker singing "Jingle Bells" in the Kids' WB! Kooky Karolfest.
The Joker is a comic book supervillain appearing in publications by DC Comics. The character was created by Jerry Robinson, Bill Finger and Bob Kane, and first appeared in Batman #1 in the spring of 1940. As the archenemy of the superhero Batman, the Joker has subsequently appeared in television programs, films, games, and on a variety of merchandise. Throughout his comic book appearances, the Joker is portrayed as a highly intelligent, master criminal. Throughout the Joker's long history, there have been several different origin tales, but the most common has falling into a tank of chemical waste, which bleaches his skin white and turns his hair green and his lips bright red. He has been repeatedly analyzed by critics as the perfect adversary for Batman; their long, dynamic relationship often parallels the concept of yin and yang.
Appearances in Christmas specials
Batman: The Animated Series
The Joker's first appearance in a Christmas special was "Christmas With the Joker", the Christmas episode of Batman: The Animated Series, which also notably marked the character's first appearance on the series (and the DC Animated Universe) in production order. In it, Joker escapes from Arkham Asylum on Christmas Eve and then hijacks all the television airwaves to broadcast his own program, Christmas with the Joker. He announces that he has taken Commissioner Gordon, Summer Gleeson, and Harvey Bullock hostage, and threatens to have them killed unless Batman can find his hideout and rescue them by midnight. In spite of the distraction of having to save a train when Joker's men destroy a rail bridge, coupled with being tricked into following a fake transmitter, Batman and Robin manage to find Joker's hideout (the Laffco Toy Factory), rescue the hostages, and bring Joker back to Arkham Asylum.
When the series was continued as The New Batman Adventures, Joker appeared in the last segment of the holiday episode, "Holiday Knights". Joker announces in a video message to Batman that he will be killing a ton of people on New Year's Eve (to make up for the fact that he will not be killing anyone next year). Batman figures that Joker will be using a sonic based weapon powerful enough to kill anyone in earshot, and will have it detonate once the bell has risen at the New Year's countdown in Gotham Square. When Batman and Robin come after him, Joker manages to capture them, but fortunately, Batman is able to short out Joker's equipment, resulting in the bomb's wires shorting out and the bell falling down, trapping Joker underneath.
Other Christmas productions
The DC Animated Universe version of the Joker also notably appeared as a member of the Warner Choir in the Kids' WB! Kooky Karolfest segments, aired in 1999. In one segment of the Karolfest, Joker sang a slightly extended version of his "personal favorite" Christmas song, the "Batman smells" variant of "Jingle Bells" (which he had notably also sang in "Christmas with the Joker"). At the end of the segment, Batman drops a cage on him.