William Arthur Stein (born February 21, 1974 in Santa Barbara, California) is a professor of mathematics at the University of Washington.
He is best known as the lead developer of Sage. He is known as a major proponent of open-source scientific software. Stein is currently doing computational and theoretical research into the problem of computing with modular forms and the Birch and Swinnerton-Dyer conjecture. [1]