Denny Slagle graduated from West Virginia Wesleyan College with a Bachelor of Science degree. Slagle became president of the construction machinery company JCB in October, 1991. After leaving JCB in 1999, Denny joined the company Volvo Construction Equipment as senior vice president of sales in 2000. Slagle became president and CEO of Volvo in January, 2003. Denny then went on to become president and CEO of Mack Trucks Inc. in April, 2008. He appeared working incognito as a plant worker at several Mack Truck manufacturing plants on the hit reality TV series Undercover Boss (2010). Slagle was named the executive vice president of sales and marketing in North and South America for the AB Volvo truck brand in January, 2012.