Burgers and toppings changed a lot over the time.
Cheeseburger & Hamburger History
The Cheeseburger was invented in Denver, Colorado, the Hamburger in New Haven, Connecticut.
Louis Ballast, born in 1910, operated the Humpty Dumpty Barrel Drive-In in Denver and was constantly looking for original ways to improve the simple meal. One day he put a slice of cheese on the burger, heated the cheese, and decided that the taste of the cheese went well with the beef.
Being excited that much he applied for a patent on his invention 'Cheeseburger' in March 1935. Anyhow, the word Cheeseburger became a quite usual and generic expression nowadays.
Those who want to pilgrimage to the cultural place of the Cheeseburger can do so by visiting 2776 N. Speer Blvd, Denver, Colorado, which is the historical site of the Humpty Dumpty which burned down completely. Today on this location you will find a quite boring parking lot here. A small memorial reminds of the Humpty Dumpty.
But: some other places in California and Kentucky doubt that this is the place where the the Cheeseburger was invented. however they never applied for the patant, and so Mr. Louis E. Ballast has to be considered the real Cheeseburger inventor. He died in 1975.
In 1900, Mr. Louis Lassen has allegedly invented the basic burger (beef in a bun) in his diner Louis' Luch, 261-263 Crown Street, New Haven. Until today, you can eat there, since his family is still operating the diner, which has been established in 1895.