Which boxer was the first undisputed cruiserweight champion in the four-belt era?

Oleksandr Usyk was the first undisputed cruiserweight champion of the four-belt era. He achieved the feat by defeating Murat Gassiev by unanimous decision on July 21, 2018, in Moscow.

The victory gave Usyk the WBA, WBC, IBF, and WBO cruiserweight titles, along with The Ring championship. It made him the first cruiserweight to hold all four major sanctioning-body belts simultaneously after the division entered the modern four-title period.

Usyk reached the final by beating Mairis Briedis in a close January 2018 semifinal. He then outboxed Gassiev with movement, timing, and accurate combinations. The tournament victory also made him the first World Boxing Super Series cruiserweight champion.

Evander Holyfield is a frequent historical mix-up. Holyfield became the undisputed cruiserweight champion in the late 1980s, but that was during the earlier three-belt era, before the WBO was generally included in the four-belt definition. Usyk later became undisputed at heavyweight as well.