Mathile graduated at age 16 from Portage High School, ranking first in his class of 14 students. He also lettered in basketball and earned an honorable mention for the all-state team. He went on to attend Ohio Northern University in Ada, Ohio, where he also played on the basketball team. He initially studied mechanical engineering before transferring to the business school. When an expected scholarship fell through, Mathile took a job pumping gas. Mathile graduated a quarter early in February 1962 with a business degree.

On July 7, 1962, he married MaryAnn Maas, the girl he had dated since high school. They have five children and live in Brookville, Ohio.

In 1970, Mathile accepted a leadership role at a small, regional pet food manufacturer: The Iams Food Company in Dayton, Ohio. To raise awareness of Iams’ product, Mathile spent weekends at dog shows, handing out samples that his children helped him package in their basement. In 1975, after shortages of ingredients almost drove the company under, Mathile purchased a 50%-ownership interest in the company from founder and owner Paul Iams for $100,000. Mathile convinced Paul Iams that the company needed to build its own manufacturing plant.

During his early tenure, Mathile oversaw The Iams Company’s rapid growth. Mathile purchased the remaining ownership shares from Iams in 1982, thus becoming its sole owner and CEO. At the time, the company had $13 million in sales.