The "Curse of Tippecanoe" takes its name from the Battle of Tippecanoe in 1811. William Henry Harrison, the governor of the Indiana Territory fought warriors of the Tecumseh Confederacy. Harrison's army attacked the Confederacy's headquarters at Prophetstown, forcing the Native American warriors to retreat and destroying the settlement. In an account of the aftermath of the battle, Tecumseh's brother Tenskwatawa, known as the Prophet, supposedly set a curse against Harrison and future presidents elected during years with the same end number as Harrison.

William Henry Harrison was elected president in 1840, took office in March 1841 and died the following month. For the next 120 years until 1960, presidents elected during years ending in a zero (occurring every twenty years) died while serving in office.

The curse, first widely noted in a "Ripley's Believe It or Not!" book was published in 1931. After the observation by Ripley, talk of the curse resurfaced as the next cursed election year approached. A cartoon feature, "Strange as it Seems" by John Hix, appeared prior to Election Day 1940, with "Curse over the White House!" A list, running from "1840—Harrison" to "1920—Harding" was followed by "1940—?" and the note that stated "In the last 100 years, Every U.S. President Elected at 20-Year Intervals Has Died In Office!"

The election of Ronald Reagan in 1980 was not followed by his death in office, despite being seriously wounded in an assassination attempt.

More Info: en.wikipedia.org