Frank Lobman though he was a heavyweight he wasn't in K-1, and K-1 only recently started around the time he was on his way out. Frank Lobman was basically the Joe Louis of Muay Thai/Kickboxing who ruled the heavyweight division with a literal iron fist despite only being 5'11" and 190 lbs soaking wet and not ripped, he had and outstanding career of 110 wins with 100 KO's a incredible 90% KO win ratio over a more impressive +100 fight undefeated streak. He had ony 6 losses all of which came after he was 38 years of age and after several surgeries recovering from injures, 3 of those losses came from a prime Peter Aerts who was approximately 4 inches taller and 40 lbs heavier and 17 years younger than Lobman (Aerts age: 21 6'3" 230 lbs, Lobman age: 38 5'11" 190 lbs). To this day Aerts has said on several occasions in many of his interviews that Lobman was one the toughest opponents he ever fought despite all the advantages that Aerts had over Lobman.
Joe Louis compendium of KO's:
Ray Robinson KO's: