John Roy Steelman ( June 23 , 1900 - July 14 , 1999 ) was the first Assistant to the President of the United States serving President Harry S. Truman from 1946 to 1953 . John Roy Steelman ( June 23 , 1900 - July 14 , 1999 ) was the first Assistant to the President of the United States , serving President Harry S. Truman from 1946 to 1953 .