The heirs of Richard Ritchie, who invented the formula for Pepsi-Cola more than 80 years ago, are suing Pepsico Inc., saying the soft drink and snack food maker has improperly interfered with their rights to their father's invention.

Ritchie was a chemist with the Loft Candy Co. when he developed his Pepsi formula in 1931. He stayed with Pepsi when it became independent, but he later joined the beverage company Cantrell & Cochrane Co. in 1962. Ritchie retired 20 years later and died in 1985.

Ritchie's daughter and son, Joan Ritchie Silleck and Robert Ritchie, sued PepsiCo on Friday, saying in the suit that they “are the rightful owners of the Ritchie invention because, inter alia, Pepsi failed to require that Mr. Ritchie transfer ownership to the Ritchie invention to Pepsi despite knowing that he had developed the Pepsi-Cola formula while working as an employee of another company.” The siblings say they want to “tell their father's extraordinary life story without interference of the threat of litigation” from Pepsi.