Russell Gerdin, founder of Heartland Express, has retired for health reasons, according to a company statement. Gerdin took a leave of absence from his duties as chairman & CEO in January.

On Friday, the company announced that Gerdin’s son Michael — who assumed his duties temporarily in January — has been permanently named chairman & CEO of the truckload carrier based in Liberty, IA. Russell Gerdin will take on the chairman emeritus title.

Russell Gerdin founded Heartland in 1978, leading the company through its initial public offering in late 1986 and through five acquisitions since 1987, with the most recent in 2002. Michael began to work at Heartland in 1992, and has served as president since 1996.

Heartland in July reported its second-quarter profit jumped 35% as revenue grew due to stronger demand for freight services, as well as the benefit of higher fuel surcharges.