The Wisconsin-based brand, famous for its fresh-never-frozen ButterBurger, opened in 1984.
Culver's was in the top 25 U.S. fast-food chains in 2020, earning $1.9 billion with 782 outlets.
The chain's restaurants are in 26 states, mostly Wisconsin on Lake Michigan's west side.
Whataburger, founded in 1950, is known for its "two-hands-needed" burger. In 2020, the brand made over $2.7 billion with 844 outlets.
Whataburger's footprint spans 14 states and will grow in the future years.
Cook Out began in 1989 and has 313 outlets in 10 states. The North Carolina-based chain is largely in the Southeast.
Milo's Hamburgers was started in 1946 by Milo Carlton, a former U.S. Officer's cook.
Carlton devised and improved "Milo's Famous Sauce" in the restaurant's first summer by using client input.