B.J. Penn = Ezzard Charles

Remembered largely as a heavyweight champion who decisioned an aging Joe Louis and battled Rocky Marciano in two gritty defeats, Charles was probably the best light heavyweight who ever lived. Yet he never won the title. Blessed with technical wizardry, he had an intuitive sense of range, timing and precision. Beating Archie Moore three out of three does not hurt his light heavyweight credentials, either. But Charles had his big-money fights against bigger men, including his 1954 battle to a decision loss against Marciano, where he had the champion badly cut. He probably would’ve won by technical knockout stoppage today.

Weighing 190 pounds in his prime, Charles gave away size and still was one of the best in the division in his day. Charles also had shocking one-punch power in his right hand, and it was said the “Cincinnati Cobra” lost much of his killer instinct after Sam Baroudi died following their 1948 match.

Penn has a similar story. Forever jumping between weight classes, he’s suddenly bored with the lightweights, despite holding the belt, and is slated to take on UFC welterweight champion Georges St. Pierre in a January rematch. If anybody can stop the Canadian juggernaut, it’s Penn, and it will be even more impressive considering he’ll be giving away a lot of natural size over a five-round fight. And while Penn’s stellar takedown defense and jiu-jitsu make him one of the trickiest fighters in the game, he also possesses a great chin, clever defense and good power in his strikes. From a technical standpoint, he has few equals in the sport.

Jake Shields = Mike McCallum

In the early to mid 1980s, boxing fans were treated to the wonderful foursome of Roberto Duran, Sugar Ray Leonard, Tommy Hearns and “Marvelous” Marvin Hagler, who all fought one another in a dizzying series of super fights that never disappointed.

Mike McCallum was an overlooked dark horse during that period who was just coming into his own, and by the time he was a big name in 1987, the foursome had largely disappeared. Hearns moved up in weight, Hagler seemingly retired and Duran knew better than to fight him. Leonard was eyeing big-name rematches with Hearns and Duran, in between picking up a payday against Donnie LaLonde in 1988.

At that time, however, McCallum would’ve been a handful for any of them. He was exceptionally smooth with top-notch skills, ring generalship and a cool demeanor, backed up by impeccable timing and a closer’s instinct.

That’s exactly the kind of fighter Jake Shields has become, as he labors in EliteXC and takes on longshot challengers. If Georges St. Pierre continues to rule the UFC’s 170-pounders in his one-sided fashion, you wonder if Shields will fall into the same no man’s land McCallum did.

Ricco Rodriguez = Riddick Bowe

Guy with tons of ability wins heavyweight title, loses focuses, gets fat and then drifts out of the picture. Sound familiar?

When Bowe won the heavyweight crown against Evander Holyfield in 1992, he was a 235-pound fighting machine, adept at battling in close -- unusual for such a big man -- or boxing your ears off with a world-class jab and thumping right hand. After two meaningless defenses against aged veterans Michael Dokes and Jessie Ferguson, he plumped up to 246 pounds for a rematch with Holyfield and lost a close decision that saw him sucking wind down the stretch.

Bowe’s weight problems dogged him throughout his career, along with stability issues, and he never regained the title.

Rodriguez -- a gifted grappler who once tapped Antonio Rodrigo Nogueira in an Abu Dhabi Combat Club submission match -- seemed to represent the next generation of heavyweight when he beat Randy Couture for the UFC title in 2002. Losing his first defense to 5-to-1 underdog Tim Sylvia, Rodriguez has since drifted around various promotions, breaking the 300-pound mark for some fights and losing to fighters who would’ve been 10-to-1 underdogs against him in his prime.

He’s still active today, but, like Bowe, you have to wonder what he could have accomplished had he stayed in shape.