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Randy Couture is the current UFC heavyweight champion. (MMAweekly.com Photo)

Some mixed martial arts fighters have been around since the very beginning, when the UFC first opened their octagon doors in 1993. Just in case you're not good with math, that's 15 years ago.

Incredibly, many of them are still fighting today, and a few are still winning. Most, however, are showing their age. While some perform an endless waltz with the end of their career, constantly going in or out of retirement, others have fallen into downward slides, suffering awful losing streaks and defeats to fighters that, years ago, they would've beaten easily.

Why do they keep fighting? Because it's an addiction. Like aging adrenaline junkies, they can't resist putting the gloves on and climbing into the cage one more time. Also, since the popularity of mixed martial arts has grown, so too have the fighters' paychecks. That's a tempting factor for fighters looking to cash in on the popularity of the sport they helped to create.

Randy Couture

While other fighters show signs of aging, Couture, who will turn 45 this year, seems to get better and better as the years pass. As the current UFC heavyweight champion, most rankings list him as the second-best heavyweight fighter in the world, with Russian Fedor Emelianenko owning the top spot. After beating both Tim Sylvia and Gabriel Gonzaga, Couture resigned from the octagon in October to pursue a fight with Emelianenko and has since been locked in a legal battle with the owners of the UFC, who contend that Couture is in violation of his employment contract. If Couture can prove his case in court, a fight with Emelianenko could happen this summer. Once it does, "The Natural" has made it clear that he plans on retiring.

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