German heavyweight boxer. He was the European Heavyweight Champion from 1964 to 1968 (retained the Title 6 times). Mildenberger fought Muhammad Ali for the World Heavyweight Title in September 1966. Mildenberger, a left-hander, frustrated the champ for most of the fight, but ultimately lost by TKO when the referee stopped the fight at 1:28 of the twelfth round following a flurry of punches by Ali.
Karl Mildenberger lost his first fight for the European Heavyweight title when he was knocked out by Dick Richardson, the Welsh boxer, in one round in April 1962. Karl rebounded with wins over Joe Erskine, Archie McBride, Joe Bygraves and a knockout win over Billy Daniels.
Mildenberger then got a draw with highly ranked Zora Folley in April 1964. Later that year Mildenberger scored a first round knockout over Sante Amonte to capture the European Heavyweight title.
He defeated Eddie Machen over ten rounds in 1966. In April 1966 Mildenberger had a five round exhibition in Sweden with former world champion Ingemar Johansson.
In 1967, Mildenberger participated in a tournament staged by the World Boxing Association to determine the new heavyweight champion after Ali was stripped of the title for refusing induction into the draft. In the first round of the tournament,getting off the deck he lost to Oscar Bonavena by a clear twelve round decision in what was proclaimed the Ring Magazine upset of the year.
Mildenberger was not the same afterwards, and was knocked out by contender Leotis Martin in seven rounds (April 1968). Subsequently, in September 1968, Mildenberger’s career ended when he lost the European Heavyweight title to Henry Cooper by eight round disqualification.
Mildenberger was the first southpaw to fight for the World Heavyweight Title.

Link to Wikipedia biography