Wasn't Wladimir in as champion at that point(?)
Unfortunately there is no undisputed heavyweight champion.
Joe Louis was World Heavyweight Champion from 1937 to 1949.
vladimir klitschko vladimir klitschko
He was world heavyweight boxing champion from 1952 until his retirement in '56.
The one and only Rocky Marciano.
Iron Mike Tyson was the youngest heavy weight champion ever at 20 years old.
John Arthur Johnson (Glaveston Giant) The first African American World Boxing Champion.