Beau Jack (born Sidney Walker; April 1, 1921 – February 9, 2000) was an American lightweight boxer and two-time world lightweight champion in the 1940s. One of the most popular fighters during the War Years, he headlined at Madison Square Garden on twenty one occasions, a record that still stands. He was considered "The greatest lightweight ever" by Cus D'Amato, famous boxing trainer and manager.