Before starting Wendy's, what fast food franchise did Dave Thomas work for?

Before starting Wendy’s, Dave Thomas worked for the Kentucky Fried Chicken franchise.

Thomas entered the restaurant business as a teenager at Fort Wayne’s Hobby House, where he learned the operations side of food service. His employer, Phil Clauss, later became an early KFC franchisee and introduced Thomas to Colonel Harland Sanders.

In 1962, Thomas was given the challenge of turning around four struggling Kentucky Fried Chicken restaurants in Columbus, Ohio. He simplified their menus, improved operations, and promoted the restaurants creatively, helping make the locations profitable. He eventually became a KFC franchise owner and regional manager for restaurants east of the Mississippi.

Thomas sold his KFC interests in 1968 and opened the first Wendy’s in Columbus, Ohio, in 1969. Some accounts also mention his brief involvement with Arthur Treacher’s before Wendy’s, but Kentucky Fried Chicken is the standard and canonical answer to this trivia question.