Oleksandr Oleksandrovych Usyk (Ukrainian: Олександр Олександрович Усик, pronounced [olekˈsɑndr ˈusɪk]; born 17 January 1987) is a Ukrainian professional boxer. He has held the undisputed heavyweight championship since 2025, and the Ring magazine title since 2022. He held the undisputed championship in two weight classes—cruiserweight and heavyweight—and is the first male boxer to become a three-time undisputed champion in the "four-belt era".

As an amateur, Usyk won heavyweight gold medals at the 2011 World Championships and 2012 Olympics while accumulating a record of 335 wins and 15 losses. He turned professional in 2013, winning his first world title in 2016. By winning the undisputed cruiserweight championship in 2018 at the conclusion of the World Boxing Super Series tournament, Usyk became the first Ukrainian undisputed champion in history. In 2021, Usyk defeated unified heavyweight champion Anthony Joshua to win the WBA, IBF, and WBO titles. In May 2024, Usyk defeated Tyson Fury to claim the WBC title and the undisputed championship in his second weight class, one of only three boxers to do so in the four-belt era. In July 2025, he knocked out Daniel Dubois to become two-time undisputed heavyweight champion, becoming the first boxer to do so since Muhammad Ali and first in the four belt era.

Usyk was the first undisputed heavyweight champion since Lennox Lewis was stripped of the title on 12 April 2000, and is the first and only cruiserweight and heavyweight boxer in history to hold the world titles of all four major sanctioning bodies—the World Boxing Association (WBA) (Super title), World Boxing Council (WBC), International Boxing Federation (IBF), and World Boxing Organization (WBO)—in the four-belt era. He previously held the undisputed cruiserweight championship from 2018 to 2019, and is the first boxer to become the undisputed champion in these two weight classes since Evander Holyfield in 1990. The Ring and the Boxing Writers Association of America named Usyk their Fighter of the Year in 2018 and 2024.

In February 2025, Sportico ranked Usyk at No. 7 among the highest-paid athletes of 2024, with an estimated income of $122 million. In May 2025, Forbes put him at No. 11 in its ranking of the highest-paid athletes in the world, with his earnings being estimated at $101 million.

Usyk was born in Simferopol, Crimean Oblast, Ukrainian SSR, Soviet Union on 17 January 1987, to parents originally from northern Ukraine. His mother was born in the Chernihiv region (in the village of Rybotyn, Korop Raion), while his father was a native of Sumy. His mother worked in construction and moved to Simferopol to study. His father was a Soviet military man who passed through Afghanistan, working as a security guard in Crimea, and the two met there.

He is the first born of his family and he has two siblings. Until age 15, he played football and was trained at the SC Tavriya Simferopol specialized sports school of Olympic reserve (club's football academy). In 2002 Usyk switched to boxing. He is a graduate of Lviv State University of Physical Culture. In his second year of school, Usyk battled life-threatening pneumonia, enduring nearly a year of illness and spending two months in the hospital before recovering.

At the 2006 European Championships he won his first three matches but lost in the semi-final to Matvey Korobov.

He then moved up to light-heavyweight later and won the Strandja Cup in 2008. In February 2008, he moved up another weight class and was sent to the Olympic qualifier in Roseto degli Abruzzi replacing European Champion Denys Poyatsyka. There he defeated world class Azeri Elchin Alizade and Daniel Price.