The concept of fried dough dates back centuries -- ancient Greeks and Romans topped their fried dough treats with honey or fish sauce, and excavations of Native American sites have turned up what appear to be fossilized doughnuts.
It's believed Dutch immigrants introduced colonial-era New Yorkers to a more modern version of the doughnut, then called olykoeks, or oily cakes.
These doughy cakes were deep-fried, but they were so thick that the middle wouldn't completely cook.
Legend has it the hole in the doughnut came about in 1847 when the Dutch sailor Capt. Hanson Gregory speared a doughnut his mother made on one of the handles of his steering wheel to free his hands. That happy accident got rid of the uncooked center, and the hole became a doughnut mainstay (Though it should be noted Gregory later claimed he cut out the center deliberately.)
Prior to the invention of the doughnut hole, it's believed some cooks, including Capt. Gregory's mother, Elizabeth, added nuts to the center of some of the treats to combat the raw dough issue.
It's believed the name "doughnut" was either a literal description of Elizabeth Gregory's treat -- dough with nuts -- or comes from the description "dough knots."
During World War I, women working with the Salvation Army helped popularize doughnuts as battlefield treats. About 250 volunteers known as "doughnut lassies" brought the fried treats to soldiers on the front lines to keep their spirits up. (The soldiers, appropriately, were known as "doughboys," but that's actually a nickname dating back to the Civil War and has nothing to do with doughnuts.)
In 1920, a Russian refugee named Adolph Levitt invented a doughnut machine to crank out the pastries more quickly at his New York bakery.
Levitt's machine was a hit. By 1931, he was making $25 million a year selling the machines, and at the 1934 Chicago's World Fair, doughnuts were called "the food hit of the Century of Progress."
One of the country's most famous doughnut retailers got its start in Depression-era Winston-Salem, N.C., in 1937. Vernon Rudolph and two of his friends used a secret recipe and borrowed to create a batch of doughnuts called Krispy Kremes, which they delivered them door-to-door.
The very first official National Doughnut Day was held by the Salvation Army in Chicago in 1938 to raise money for the group during the Great Depression. The Salvation Army also used it to commemorate the World War I doughnut lassies. The group remains active in National Doughnut Day today.
Doughnuts once again became patriotic fare during World War II. That time it was Red Cross workers known as "doughnut dollies" who were handing out doughnuts to troops on the front lines.
In 1950, Bill Rosenberg opened a shop called Dunkin' Donuts in Quincy, Mass., that served fresh donuts and a proprietary blend of coffee. The first franchise was licensed in 1955, according to the company.
Today, Dunkin' Donuts has more than 11,000 stores in 33 countries. Krispy Kreme has more than 800 locations in 22 countries and also sells its doughnuts in 10,000 other stores, according to the company. And both franchises are giving out free doughnuts to celebrate National Doughnut Day (though at Dunkin' Donuts, you do need to buy a drink).