Floyd Mayweather is widely acknowledged to be the best pound-for-pound fighter in the world.
However, it's fair to wonder if he really is deserving of the unofficial honor.
Since the end of 2007, a year in which Mayweather defeated Oscar De La Hoya and Ricky Hatton, he has fought four times in six years. Three of those victories were decisions, and the only stoppage was a four-round controversial knockout over Victor Ortiz in 2011.
When Mayweather has been at his best in his career, he ranks with the greatest names in boxing history. He is a master in the ring with speed, quickness, instincts, defensive skills and the ability to exploit any weakness that he senses in his opponent.
His peers among the all-time greats may be Sugar Ray Robinson, Muhammad Ali, Joe Louis, Henry Armstrong, Roberto Duran, Willie Pep and Julio Cesar Chavez.
That was when Mayweather was in his prime. What about now?
Mayweather is 35 years old. To say he has has been selective in his fights since taking off two years from the end of 2007 and 2009 is an understatement.
He has done enough in the ring to say that it would still take a substantial effort for any of the game's best fighters to beat him.
However, if you look at many of the top fighters who could conceivably get in the ring with Mayweather, it no longer seems inevitable that he would emerge with a convincing win—or a win of any kind—against opponents like Nonito Donaire, Andre Ward or Sergio Martinez.
He would seem to have an edge over Juan Manuel Marquez—whom he defeated in 2009—but it seemed as if Manny Pacquiao had an edge on Marquez as well until he got knocked out in their fourth bout.
For that matter, if Pacquiao decides to remain an active fighter and can register a comeback victory, could the long-discussed fight with Mayweather become reality?
Mayweather's undefeated record may be the ticket he believes that links him to the greatest fighters in the history of the sport. He has a 43-0-0 record with 26 knockouts, but the sport's best representatives have all tasted defeat.
Other than Rocky Marciano—who is generally not considered among the all-time greats—the best fighters all tasted defeat from time to time and showed they could bounce back.
There's a certain resiliency that the great fighters have proven they had after tasting defeat. Would Ali's victories over George Foreman and Joe Frazier have meant as much if he hadn't been beaten by Frazier in their first bout?
Would there have been as much made of Louis's destruction of Max Schmeling if he hadn't been beaten by his rival in their first bout?
This is not to say that it would benefit Mayweather if he lost a fight or got knocked out. But coming back from a defeat would give his career a dimension he has not demonstrated.
He has avoided many of the best fighters. Nobody is saying he is afraid of Pacquiao, Ward or Martinez, but he has not embraced opportunities to make such bouts.
That works against Mayweather.
In the end, these are minor flaws and questions. He has been the greatest fighter of his era. He deserves to hold on to that assessment until he gets outclassed in the ring by a top-flight opponent.
Father time will catch up with Mayweather eventually. But to this point, he has managed to survive and thrive.
Any opponent that wants to be called the best pound-for-pound fighter is going to have to take that unofficial designation away from Mayweather.
He has agreed to put his WBC welterweight crown on the line in May against a yet-to-be-determined opponent. If it's against one of the sport's elite fighters, it will mean that his pound-for-pound title is on the line, too.