Who invented the burger?
Nobody knows for sure. The patty was probably brought to the United States by 19th century German immigrants, and several American towns claim the first burger, with New Haven's Louis Lassen the best known.
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A name from Hamburg
Start with the name. Hamburger points to Hamburg, the big German port, and Britannica says the patty and the sandwich were probably brought to the United States by German immigrants in the 1800s. Beyond that, Britannica is blunt: the origin of the hamburger is unknown. Within a few decades of arriving, though, it was seen as the most American food there is. That gap between a German name and an American icon is where all the arguing starts.
The fair stand claims
Two claims go back to 1885. In Seymour, Wisconsin, people credit Charlie Nagreen, known as Hamburger Charlie, who is said to have pressed meatballs flat between bread at the Seymour Fair so visitors could eat while walking. In the same year the Menches brothers say they made the first one at the Erie County Fair in New York. In Athens, Texas, Fletcher Davis is said to have sold burgers at his café in the late 1880s and shown them at the 1904 St. Louis World's Fair.
Louis' Lunch in New Haven
The claim with the most paperwork belongs to Louis Lassen. He ran a lunch wagon on Meadow Street in New Haven, Connecticut, from 1895, feeding factory workers. The story says that in 1900 a customer asked for something quick, and Lassen put a ground beef patty between slices of toast. In 2000 the Library of Congress recorded him as the creator, after a push by Congresswoman Rosa DeLauro. Sources even disagree on his year: some versions of that record say 1895, Louis' Lunch says 1900.
Legend versus evidence
Here is the honest part. ConnecticutHistory.org notes that the rival claims from Texas, Hamburg in New York and Seymour rest on oral history rather than documents. But Louis' Lunch still serves its burger on toast, not a bun, and Oklahoma says the bun is the whole point. In 1995 its governor proclaimed that Oscar Bilby of Tulsa served the first burger on a bun, on the Fourth of July 1891. So the winner depends on what you think a burger is.
From lunch wagon to everywhere
What turned the burger into a global habit was business, not invention. Walter Anderson, who is credited with a burger bun in 1916, co-founded White Castle in 1921. Chains like McDonald's, Burger King and Wendy's then spread the burger around the world. Louis' Lunch is still open in New Haven, at 263 Crown Street, and the Lassen family still cooks on a broiler dated 1895. A typical burger today is one beef patty in a soft bun, plus whatever you pile on top.