Simplify the following text for a Grade 8 native English-speaking person.
Original: James Rodney Schlesinger ( born February 15 , 1929 ) was United States Secretary of Defense from 1973 to 1975 under presidents Richard Nixon and Gerald Ford .
Simplified: James Rodney Schlesinger ( born February 15 , 1929 ) is an American politician . He is best known for serving as Secretary of Defense from 1973 to 1975 under Presidents Richard Nixon and Gerald Ford .