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
From April 5, 1915 to July 4, 1919 - Heavy weight boxing champion - Jess Willard ( American )
He was world heavyweight boxing champion from 1952 until his retirement in '56.
The one and only Rocky Marciano.