Slurpees, like so many other genius inventions, were created on accident. When Dairy Queen owner Omar Knedlik's soda fountain broke in the late 1950s, he improvised and put bottles of soda in the freezer to stay cold. He accidentally left them in a little too long, and they had frozen into a slushy consistency by the time his customers bought the sodas. To his surprise, they loved this new slushy soda and started requesting "those pops that were in a little bit longer."
Knedlik built a machine to accommodate his new hit snack using the air conditioning unit from a car. The machine worked by combining and freezing a flavor mix, water, and carbon dioxide to make it fizz. He held a contest to help name the product and the winning entry was ICEE. The ICEE machine was redesigned and sold to a few stores throughout the early 1960s.
In 1965, 7-Eleven licensed the machine. The name was changed to Slurpee to make it unique to 7-Eleven. "Slurpee" was coined by Bob Stanford, a 7-Eleven ad executive when he described the sound made while sipping it through a straw.