Konstantin "Kostya" Tszyu (Russian: Константин «Костя» Цзю) is a Russian Australian former professional boxer who competed from 1992 to 2005. He held multiple light-welterweight world championships, including the undisputed and lineal titles between 2001 and 2005. Tszyu was an exceptional all-around boxer-puncher who relied heavily on accuracy, timing, and carried formidable punching power; he is often regarded as one of the hardest-punching light-welterweights in the division's history.