Although both combat sports, boxing and mixed martial arts have mostly remained segrated. Athletes have mostly stayed in their own sport and their seems to be a different fan base for each. Boxing is somewhat considered your father's sport and MMA is for the new generation. UFC President Dana White considers himself a fan of both and has often praised some of boxing's brightest stars.
No MMA athlete has truly crossed over to a sucessful boxing career and no boxer has really tried to make a real run at MMA. In 2010 heavyweight James Toney did a one fight stint in the UFC, losing to hall of famer Randy Couture in the first round after being taken down easily.
Recently another boxing champion has brought up the idea of crossing over, going as far as talking to White about a possible career in the UFC. He recently spoke to Erik Fontanzez of Yahoo Sports about the possibility:
Two-time welterweight boxing champion Andre Berto discussed potentially fighting in the UFC with the organization's president, Dana White, a company official confirmed on Friday.
The fighter said in a recent interview that he ran into White a few weeks ago in Los Angeles, and the two had a conversation about the boxer transitioning over to the Las Vegas-based MMA promotion.
"I talked to Dana White about this ... the last time I [saw] him," Berto said in a recent video. "Don't be surprised if I try to get in that thing and win a title. I'll be the first fighter to win a boxing championship and a UFC mixed martial arts world championship."