National Underdog Day is observed worldwide every third Friday of December, celebrating individuals and groups who achieve unexpected victories against the odds. The holiday was founded in 1976 by Peter Moeller in Clio, Michigan, for Chase’s Calendar of Events, with the aim of honoring unsung heroes and encouraging support for those typically expected to lose. The term "underdog" has its origins in 19th-century dog fighting, where the losing dog was referred to as the underdog. Cultural references, such as the biblical story of David and Goliath, highlight the reverence for underdogs, as do modern examples like the U.S. hockey team's "Miracle on Ice" victory in 1980 and Susan Boyle's success on Britain's Got Talent. Celebratory activities include watching underdog-themed movies and sharing personal underdog stories on social media using hashtags like #NationalUnderdogDay.