According to the passage, who first had the idea of making hamburgers?

Everybody knows the hamburger is a very popular American food. However, people in the United States learned to make hamburgers from Germans, and Germans got the idea from Russia. In the thirteenth century the Tartar people from central Asia moved into Russia and parts of Europe. They fought the Russians and won. They ate something like hamburger meat but it was raw. This raw meat was beef, goat meat or horse meat. Soon the Russians started to eat raw meat too. Germans from Hamburg and other northern cities learned to eat this food from the Russians. However, they added pepper, a raw egg, and then cooked it. Between 1830 and 1900, thousands of Germans went to live in the United States.  They took the hamburger with them.  People called it hamburger steak.In 1904o at the World’s Fair in St Louis, a city on the Mississippi River, a man from Texas sold hamburger steak in a roll. Then people could eat it with their hands, like a sandwich.  This was the first real hamburger like the hamburgers we eat today.Today some people still like to eat raw beef. They call it "steak tartar".