Yuri Boyka is the main antagonist in Undisputed 2: Last Man Standing and the main protagonist in Undisputed III: Redemption and Boyka Undisputed IV. He is a Russian prisoner who is in jail for a murder of three people. In the prison he participates in a series of illegal full-contact Mixed Martial Arts matches and dominates them until he faces George Chambers who defeats him and injures him. Several years later Boyka participates in an international tournament of prison fighters.