The Treehouse of Horror are a series of episodes in the animated series The Simpsons. They are Halloween specials, each consisting of three separate, self-contained segments. These segments usually involve the Simpson family in some horror, science fiction, or supernatural setting. Considered non-canon, they always take place outside the normal continuity of the show and completely abandon any pretense of being realistic. The first Treehouse of Horror episode aired on October 25, 1990 as part of the second season and was inspired by EC Comics horror tales. The episodes are known for being far more violent and much darker than an average Simpsons episode. As of 2008, there are 18 Treehouse of Horror episodes, with one airing every year, and the newest episode, "Treehouse of Horror XIX", is scheduled to air on November 2. Episodes contain several trademarks, including the alien characters Kang and Kodos, "scary names" in the credits, a special version of the opening sequence, and parodies of horror and science fiction films. The show's staff regard the Treehouse of Horror as being particularly difficult to produce as the scripts often go through many rewrites, and the animators typically have to design new characters and backgrounds.

According to traditional accounts, Martin Luther nailed his Ninety-Five Theses onto the door of a church in Wittenberg, Germany, marking the beginning of the Protestant Reformation.
(http://en.wikipedia.org/wiki/Martin_Luther)

Leiden University Library in Leiden in the Netherlands, one of the cultural centres that gave direction to the development and spread of knowledge during the Age of Enlightenment, opened its doors after its founding in 1575.
(http://en.wikipedia.org/wiki/Leiden_University_Library)

The 60-foot (18 m) colossal busts of U.S. Presidents George Washington, Thomas Jefferson, Theodore Roosevelt, and Abraham Lincoln at Mount Rushmore, created by artist and sculptor Gutzon Borglum, were completed.
(http://en.wikipedia.org/wiki/Mount_Rushmore)

Indira Gandhi, India's first and to date only female prime minister, was assassinated by two of her own bodyguards, sparking riots in New Delhi and several other cities throughout the country.
(http://en.wikipedia.org/wiki/Indira_Gandhi)

Singapore Airlines Flight 006 collided with construction equipment while attempting to take off from Taiwan's Chiang Kai-Shek International Airport during heavy rain, killing 79 passengers and 4 crew members.
(http://en.wikipedia.org/wiki/Singapore_Airlines_Flight_006)

Ragnarok: (n) (Norse mythology) The final battle between gods and giants, involving all creation which denotes the end of the world as it is known and almost all life.
(http://en.wiktionary.org/wiki/Ragnarok)

He who has provoked the lash of wit, cannot complain that he smarts from it.
--James Boswell
(http://en.wikiquote.org/wiki/James_Boswell)