Determined to challenge the growing American military presence in their territory, Native Americans in northern Wyoming lure Lieutenant Colonel William Fetterman and his soldiers into a deadly ambush on December 21, 1866. With 81 fatalities, the Fetterman Massacre was the army’s worst defeat in the West until the Battle of Little Bighorn in 1876.

On December 21, 1954, Dr. Sam Sheppard is convicted for beating his wife, Marilyn, to death inside their suburban home in Cleveland, Ohio five months earlier. Sheppard claimed to have fallen asleep in the family’s living room and awakened to find a man with bushy hair fleeing the scene. The authorities, who uncovered the fact that Dr. Sheppard had been having an affair, did not believe his story.

The film The Graduate opens at two theaters in New York: the Coronet on Third Avenue and the Lincoln Art Theater on Broadway. The film, based on a 1963 novel by Charles Webb, had a simple premise: As its screenwriter explained it, “this kid graduates college, has an affair with his parents’ best friend and then falls in love with the friend’s daughter.” (It was, he added, “the best pitch I ever heard.”) In other words, The Graduate was an uneasy exploration of what it meant to be young and adrift at a time of extraordinary confusion and upheaval. Anne Bancroft and Dustin Hoffman starred.

Apollo 8, the first manned mission to the moon, is successfully launched from Cape Canaveral, Florida, with astronauts Frank Borman, James Lovell, Jr. and William Anders aboard.

Wealthy socialite Martha “Sunny” Crawford von Bulow is found in a coma—the result of what appeared to be an insulin overdose—on the marble bathroom floor of her Newport, Rhode Island, mansion. Following a long investigation, Sunny’s husband, Claus von Bulow, was charged with two counts of attempted murder and was convicted in a sensational trial in 1982. But the conviction was later overturned, and Claus was acquitted at a second trial in 1985.

On December 21, 1996, Margret Rey, who with her husband Hans created the popular Curious George children’s books about a mischievous monkey, dies at age 90 in Cambridge, Massachusetts. The Reys, both German Jews, escaped wartime Europe in 1940 and fled to America. The following year, the first Curious George book was published in the United States.

On December 21, 2012, the music video for "Gangnam Style," a song by the Korean rapper Psy, becomes the first YouTube video to garner one billion views. The video's global popularity is a case study in the power and unpredictability of viral internet content.