Trevor Berbick (TKO2) - 1986 Tyson was 20 Years Old.
Trevor Berbick On November 22, 1986, Tyson was given his first title fight against Trevor Berbick for the World Boxing Council (WBC) heavyweight championship. Tyson won the title by second round TKO, and at the age of 20 years and 4 months became the youngest heavyweight champion in history
He defeated Alberto Del Rio to win the World Heavyweight champion.(The title Edge retired)
1964, 1974 and 1978
Brock Lesnar won the heavyweight title match at the UFC 116 event. Shane Carwin was the interim heavyweight champion and Lesnar was the reigning heavyweight champion. So, this bout was the title unification fight. Lesnar defeated Carwin to become the undisputed champion.
WWE Champion Randy Orton def. World Heavyweight Champion John Cena to become WWE World Heavyweight Champion (Tables, Ladders and Chairs Match)
R-Truth has not become WWE World Heavyweight Champion (formerly the WWE Championship).
no one knows