James Hagler was born in Brockton, Massachusetts. He is the son of Marvelous Marvin Hagler, who reigned as the undisputed middleweight champion from 1980 to 1987. He is the eldest out of the Hagler 5 (children). He has three kids of his own (James Jr is a pro fighter who is 3.1ko. with no losses and 1 default). His brother, Rockin’ Robbie Sims, who is James’s uncle KO’d an inexperienced Iran Barkley, fought an exhilarating fight against Bobby Chaz, and rose to prominence as a middleweight contender by defeating Roberto Duran in 1986. Both brothers were trained by the famous Brockton-based trainers Pat and Goody Petronelli.
James Hagler’s family always had a special relationship with boxing, with his father, Marvelous Marvin Hagler, and Uncle Robbie Sims achieving great success in the sport. As a child, James was always closely involved with boxing, and it wasn’t long before he began developing a passion for it himself.
James Hagler had always dreamed of becoming a fighter and making it to the Olympics. He worked hard and trained diligently to achieve his goal, but he never had the support of his father. Despite this, James was determined to succeed and make a name for himself in the boxing world.