Fedor or GSP. The latter is more well rounded, beat all generations during his career, and went out on top by winning the belt a division above. Fedor went 10 years without a loss @ HW. In MMA. That's absolutely insane. Either man holds the crown. Honourable mention goes to Frank Shamrock, though. He was the prototype for what we see today. And his fight with Tito is legendary, because Tito was running through the Lions Den crew until he met Frank...