Allen left Microsoft in 1983, before the company became a corporate juggernaut, following a dispute with Gates, but his share of their original partnership allowed him to spend the rest of his life and billions of dollars on yachts, art, rock music, sports teams, brain research and real estate.
Allen died from complications of non-Hodgkin's lymphoma, a type of cancer, the Allen family said in a statement.
Bill Gates described Allen as following the Microsoft partnership with a "second act" focused on strengthening communities and in a statement said, "I am heartbroken by the passing of one of my oldest and dearest friends."