 He soon met legendary UFC and PRIDE FC fighter Mark Coleman who had a better plan for the young Sims which was to become a mixed martial artist, believing that Sim's huge size advantage would be significant against opponents.Sims helped Coleman prepare for his bout with Ricardo Morais at PRIDE 8, before embarking on his own career in the sport.In 2003, Sims fought a controversial fight against Frank Mir at UFC 43.