Since deceased or living wasn't specified, there's both on mine:
- "Sugar" Ray Robinson. Given today's training, supplementation of, ummmm, various types, nutrition and technology, he would be completely untouchable 3 - 4 weight either way. It pisses me off hearing Rogan say Mayweather Jr. is the greatest of all - time. He might be top five all - time when it comes to defense, but as an overall, complete boxer I don't think he even cracks the top 10. "Sugar" Ray Robinson is hands - down the best boxer to ever enter the ring and would've eaten the big 4 in the 80's for lunch, not to mention the boxers of the 90's all the way up to today.
- Alexander Karelin. Upcoming opponents of his would oftentimes concede the match before it even started because they knew what the outcome would be, no matter how much they gave. I was happy to see Rulon Gardner, a good ol' American country boy, finally put an end to his reign of terror. The ironic part of that though was he achieved that victory by exploiting a rule the IOC had recently implemented that negated one of Karelin's most dominant maneuvers, because he was so many levels above his competition that nobody could even score a point on him.
- GSP. I did not want to pick more than one competitor per sport, so Muhammad Ali, John Smith, Dan Gable and Dave Schultz were unfortunately left out (yes, I know Smith, Gable and Schultz wrestled free and Karelin was Greco-Roman, but they are both still wrestling). I struggled with who my third guy was going to be. I narrowed it down to GSP and Jon Jones. But between Jon pissing hot multiple times, being pulled from cards for other reasons and here lately looking like he really doesn't care that much, I had to go with GSP. He's never pissed hot, his discipline, work ethic and training are above any other MMA fighter in the world and he's humble and constantly wanting to challenge himself harder. The fact that he was out all those years, came back, went up a weight and won the middleweight championship by finishing a game as fuck Bisping was something only a handful of guys in MMA history could have probably accomplished.