- Aristotle Socrates Onassis (/oʊˈnæsɪs/, US also /-ˈnɑː-/; Greek: Αριστοτέλης Ωνάσης, romanized: Aristotélis Onásis, pronounced [aristoˈtelis oˈnasis]; 20 January 1906 – 15 March 1975) was a Greek and Argentine business magnate. He amassed the world’s largest privately-owned shipping fleet and was one of the world’s richest and most famous men. He was married to Athina Mary Livanos, had a long-standing affair with opera singer Maria Callas and was married to American former First Lady Jacqueline Kennedy.