Aristotle Socrates Onassis (; Greek: Αριστοτέλης Ωνάσης, Aristotelis Onasis; 20 January 1906 – 15 March 1975), commonly called Ari or Aristo Onassis, was a Greek shipping magnate who amassed the world's largest privately owned shipping fleet and was one of the world's richest and most famous men. He was known for his business success, his great wealth and also his personal life, including his marriage to Athina Mary Livanos (daughter of shipping tycoon Stavros G. Livanos); his affair with famous opera singer Maria Callas; and his 1968 marriage to Jacqueline Kennedy, the widow of American President John F. Kennedy.
Onassis was born in Smyrna and fled the city with his family to Greece in 1922 in the wake of the Greco-Turkish War. He moved to Argentina in 1923 and established himself as a tobacco trader and later a shipping owner during the Second World War. Moving to Monaco, Onassis fought Prince Rainer III for economic control of the country through his ownership of SBM and its Monte Carlo Casino. In the mid 1950s he sought to secure an oil shipping arrangement with Saudi Arabia, and engaged in whaling expeditions. In the 1960s Onassis attempted to establish a large investment contract, Project Omega, with the Greek military junta, and sold Olympic Airways which he had founded in 1957. Onassis was greatly affected by the death of his 24-year-old son, Alexander, in a plane crash in 1973, and died two years later.