The invention of the hamburger is debated with multiple claimants, but it originated in the United States in the late 1800s or early 1900s. Key figures often credited include:

• Charlie Nagreen from Wisconsin, who in 1885 reportedly flattened a meatball and placed it between two slices of bread for easier eating at a fair.
• Louis Lassen, a Danish immigrant in New Haven, Connecticut, who in 1900 is said to have placed a beef patty between slices of bread, creating the first hamburger sandwich.
• Frank and Charles Menches, brothers who claimed to have invented the hamburger in 1885 at a fair in Hamburg, New York, after running out of pork sausage and substituting ground beef.
• Oscar Weber Bilby of Oklahoma, who in 1891 is credited with serving the first ground beef patty on a bun.

There is no single definitive inventor, as similar ideas emerged independently in different locations in the U.S. around that time, contributing to the evolution of the modern hamburger.