Marvin Hagler. Maybe the greatest middleweight of all time. 62-3-2. He lost 2 fights earlier in his career and became one of the most dominant fighters of all time, losing only once more on a decision to Ray Leonard. Tyson, Lewis, Holyfield, Holmes, Ray Leonard, Duran, Roy Jones. All great fighters, but all have been knocked out. I don't if Holmes would have been knocked out had he not been 38 when he fought Tyson.