Ari Onassis was a Greek shipping magnate and billionaire who was married to Jacqueline Kennedy, the widow of President John F. Kennedy. He was known for his close friendships with many famous people, including Aristotle Onassis, his father, and Aristotle's close friend, Stavros Niarchos. Onassis was also known for his philanthropy, donating large sums of money to charities and causes around the world.