Probably the most obvious on this list, Lesnar gets an unfair bad rap for his MMA run. Lesnar left the WWE in 2004, with hopes of an NFL career. Ultimately, his age proved to be too much of a hurdle, and would return to wrestling in Japan shortly thereafter. In 2007, Lesnar made his MMA debut, crushing MIn-Soo Kim. After just one fight, he was signed by the UFC, and booked against former UFC Heavyweight champion Frank Mir. Lesnar lost a controversial bout to Mir, before steamrolling Heath Herring and Randy Couture on his way to winning the UFC Heavyweight championship. Lesnar still actually holds a UFC record, successfully defending his heavyweight title twice. Lesnar also participated in UFC 100, the highest selling UFC pay-per-view of all time, headlining the bout against rival Frank Mir in a UFC title re-match. Lesnar would later suffer from diverticulitis and be forced to retire.