William H. Diddel attended Wabash College in Indiana, where he was considered a great college athlete. Outside of being a multiple sport athlete at Wabash College, Diddel also won five Indiana State Amateur Championships in golf. Due to his polished golf background, Highland Golf and Country Club asked him to finish a new course routed by Willie Park Jr. After completing the project in 1922, it motivated him to become a full-time architect.

Diddel was responsible for the design of more than 75 golf courses, focusing on Indiana and the Midwest.

There were many notable characteristics that shaped Diddel as an architect. He was considered to be an innovator; with many projects having small budgets, he was able to create challenging golf courses without features like sand bunkers or ability to shape or contour fairways and greens. Another strong characteristic was Diddel’s patience as an architect. He was noted to never display any sort of negative emotion, even when golf clubs would back out of their agreements with him.

Diddel was one of the 14 founding members of ASGCA in 1947 and served as ASGCA President in 1954-1955 and in 1965-1966. He served as an ASGCA member for 38 years until his death in 1985.