In his day, Dr. Riddle was considered one of the top biologists in the United States. He was best known for pituitary gland and hormone research. His research on prolactin had him featured on the 9 Jan 1939 cover of Time magazine.
In 1958, Dr. Riddle was named the Humanist of the Year by the American Humanist Association.
He died on 29 Nov 1968 and he is buried in Grandview cemetery in Bloomfield, Greene Co., Indiana.
A copy of Time magazine, 9 Jan 1939 is on display at the library.