Aristotle Socrates Onassis ( January 15 , 1906 - March 15 , 1975 ) was a prominent Greek shipping magnate and founder of Olympic Airways . Aristotle Sokratis Onassis ( , Aristotelis Onasis ; 15 January 1906 -- 15 March 1975 ) , commonly called Ari or Aristo Onassis , was a prominent Greek shipping magnate of the 20th century .