Konstantin Borisovich "Kostya" Tszyu (/ˈkɒstə ˈzuː/ KOS-tə ZOO; Russian: Константин Борисович «Костя» Цзю, IPA: [kənstɐnʲˈtʲin bɐˈrisəvʲɪtɕ ˈkosʲtʲə ˈdzːʲu]; born 19 September 1969) is a Russian-Australian former professional boxer who competed from 1992 to 2005.

In 1995, Tszyu won his first of many professional world championships at light-welterweight—the International Boxing Federation (IBF) title—by defeating Jake Rodríguez.

Tszyu was born in Serov, a town near the Ural Mountains, in the former Soviet Union to a Korean (paternal)–Mongol (maternal) father and a Russian mother.

[5] As a child, Kostya was hyperactive, so his father decided to take him to a boxing gym, where he would channel that energy by fighting older boys.

[7] Tszyu was a member of the Soviet Army, but since he was selected as an elite athlete, he was not required to serve the ordinary duty.

Following the collapse of the Soviet Union in 1991, early the next year, Tszyu emigrated to Australia with his girlfriend, where they married in 1993 and became Australian citizens, settling in Sans Souci, Sydney.

Before marrying her, though, Tszyu had already turned professional, beating Darrell Hiles by a knockout in one round on 1 March 1992, at Melbourne.

Immediately at the Championships he was approached by local boxing promoters, deciding to pass up the 1992 Summer Olympics in favor of a professional career.

A week later he signed with Australian promoter Bill Mordey as his manager and Johnny Lewis as his trainer in Sydney.

In his fourth professional bout, he met the former WBC Featherweight Champion Juan Laporte, decisioning him over ten rounds.

In 1994, Héctor López, Angel Hernandez (who had just come off of a loss after challenging Julio César Chávez for the WBC belt), and Pedro Chinito Sanchez from the Dominican Republic tried to beat Tszyu, but Tszyu beat Lopez by a decision in ten, Hernandez by a knockout in seven, and Sanchez by a knockout in four.

In 1995, he received his first world title shot when he fought IBF Light Welterweight Champion Jake Rodríguez at Las Vegas, Nevada.

In a controversial decision, referee Joe Cortez judged that it was an "unintentional illegal blow", believing it to be shortly after the bell.

Kostya was interviewed by Ray Wheatley on YouTube in 2011 and stated he regards his win over Miguel Angel Gonzalez as his best ever performance.

Tszyu finished 2001 by recovering his IBF belt in a unification bout with the current champion Zab Judah, by a knockout in the second round.

Tszyu in 2002 had only one bout, beating the top-ranked contender of all three of his belts, Ben Tackie of Ghana by a decision in twelve rounds.

On 19 January 2003, Tszyu began the year by retaining his title against former world champion Jesse James Leija by a knockout in six.

He next fought on 5 June 2005, against British boxer Ricky Hatton, Tszyu lost this fight and his world title by RTD (Referee technical decision) after retiring on his stool at the end of the 11th round.

During the show, he denied his retirement and said he would return if a fight with Shane Mosley, Manny Pacquiao or Floyd Mayweather Jr. could be made.