20. Jon Jones
Bonafides From 2002-2012: UFC Light Heavyweight Champion, Former USKBA Light Heavyweight Champion, 15-1-0 (8 KOs, 5 Submissions)
Jon Jones was named Fighter of the Year by ESPN last year 2011, he currently holds the UFC Light Heavyweight Championship, and he's already captured a nation of MMA fans with his unorthodox fighting style. All of this and he's only 24 years old. The biggest challenge of his career is coming when he meets Rashad Evans in the Octagon on April 21, 2012 in UFC 145, but hey, Bones has turned doubters into believers before.