By Iron Mike Gallego

On Dec. 16, Vitali Klitschko, one half of the towering pair of Ukrainian siblings that have dominated boxing's heavyweight division for the last decade, officially vacated his title to focus on a career in politics. A 42-year-old fighter who had not entered the ring for more than a year stepping away from the sport is usually not newsworthy. But in this case, the implications are potentially huge. The lineage that connects Jack Johnson to Lennox Lewis and John L. Sullivan to Mike Tyson to present day -- a tissue that is held intact by the thinnest of threads -- may finally be coming undone.

The issue is not the loss of Klitschko himself, a serviceable but historically unremarkable heavyweight champion, but what it means for the sport. Norman Mailer once wrote that "the heavyweight champion of the world is either the toughest man in the world or he is not, but there is a real possibility he is." With Vitali Klitschko's retirement, that possibility -- the possibility at the core of the heavyweight legend -- may be hopelessly outdated. To understand why that is, we must place the last decade of heavyweight boxing in its proper context.

Klitschko inherited his title in 2004 after the great champion Lennox Lewis retired and vacated his belts. Lewis had stopped Klitschko the year before in a surprisingly competitive fight in which Klitschko led on all cards before a deep gash on his eye forced the doctor to end the match. The fight, however, was not as close as it seemed. Lewis showed up looking flabby and disinterested, weighing in at a career-high 256 pounds, seven more than his previous fight. Against Klitschko, Lewis's poor condition took its toll early, though he had begun to take control before the stoppage. If even that version of Lewis was still good enough to beat Vitali, it surely said something unfavorable about the Ukrainian's ceiling.

At the same time, Klitschko's brother Wladimir was dealing with issues of his own. Once the top prospect in the sport, the former Olympic gold medalist had seemingly come apart at the seams. On two occasions in a little over a year, and for the third time in his career, Wladimir had been badly knocked out by unheralded competition. Even his winning efforts seemed to be drama-filled: Against Samuel Peter, a hulking but unskilled opponent, Klitschko was floored three times en route to eeking out a narrow decision win.

Then, something truly remarkable happened for both brothers: They became unbeatable. Since Vitali's loss to Lewis, and Wladimir's win over Peter, the two have dominated every opponent, with barely a moment of drama along the way. How on Earth did this happen?

One reason is that winning builds confidence, and it is sometimes said that a new champion will be 15-20% better in his first defense as a result. Moreover, the Klitschkos modified their style to be more defense-oriented, much to the chagrin of the boxing public. Both brothers have a tendency to lean backwards and wing long jabs to keep their opponents at bay. While the style hardly harkens back to the grace of Muhammad Ali or the savagery of Mike Tyson, it has proven effective at protecting the Klitschkos fragile chins.

Another part of the brothers' success? The sorry collection of stiffs they've dismantled over the past decade. Neither Vitali nor Wladimir has entered the ring as anything other than an overwhelming favorite during their run atop the division. Prince Fielder is unlikely to set any speed records, but match him in a sprint against a field of septuagenarians who have recently received hip replacements, and he'll look like Carl Lewis. In much the same way, the Klitschkos have benefitted from historically weak opposition. Rather than being the "toughest man [or men] on the planet," the two Klitschkos have merely been tougher than their peers.

An underwhelming heavyweight champion is not unprecedented. After the glorious 1970s with Muhammad Ali, Joe Frazier, George Foreman and Larry Holmes came a dry spell in the early 1980s where guys with names like Michael Dokes, John Tate, Pinklon Thomas and Tim Witherspoon held titles before Tyson, Evander Holyfield and Lewis arrived and restored order. But there are no Tysons, Holyfields or Lewises waiting in the wings in 2013 (other than the actual Holyfield, who at 51 is still hinting that he wouldn't mind a fight). 

The late famous boxing historian Bert Sugar once observed that the best American heavyweight prospects today choose to play football instead (Ray Lewis and Brian Urlacher were among those he highlighted). Outside the U.S., basketball and rugby tend to attract most of the large, athletically talented youth. And for the truly pugnacious, MMA proves to be an enticing option, particularly for those who grow up in developing countries, where martial arts studios are far more prevalent than boxing gyms. Put simply, no matter who you are or where you live, if you are 6-foot-5, muscular and athletic, a career in boxing is no longer at the top of your to-do list.

To compound matters, the sport no longer depends upon the heavyweight, anyway. In recent years, Oscar De La Hoya and Floyd Mayweather have outsold the largest heavyweight fights in history. True, neither man has captivated the general public's attention in quite the same way that the last great heavyweights did, but the modern economics of boxing no longer require that level of mainstream interest. It is certainly easier and more profitable for promoters to target the million or so hardcore fans that will plunk down $65 for a pay-per-view card than to cast a wide net and hope that the broadcast networks will get back into the boxing business. The marquee heavyweight is an obsolete luxury item.

Despite his shortcomings, Vitali Klitschko was a final link to the glorious past of heavyweight boxing. He at least rumbled with a true champion and proved that the two men belonged in the same ring. Now his brother Wladimir becomes champ, not because he beat the best or even stood in with them, but because he is the best of what's left. And Wladimir is 38 years old, with a pretty Hollywood fiancée, and a successful promotional company to run. There's no reason to expect him to continue much longer.

In 2013, the heavyweight champion is no longer the most feared or respected man in sports; he isn't even taken seriously. Even Hollywood has gotten in on the joke. Rocky returned to the ring this year, but he did so as a punch line. The heavyweight division will continue, and there will be more people who own heavyweight belts, but there may never be another true heavyweight champion. 

Down goes Frazier. This time, I fear it's for good.

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Iron Mike Gallego is the online identity of a passionate boxing fan. IMG is an occasional contributor to Deadspin, where he has written about topics ranging from boxing to champagne, and can regularly be found on twitter @ironmikegallego.