Jae C. Hong, Associated Press
Welterweight champ Floyd Mayweather Jr. says he's lost his passion for boxing.

Although Floyd Mayweather Jr. has retired at least twice before, boxing's pound-for-pound king says he's really taking off his crown this time.

Mayweather abruptly retired Friday at the peak of his athletic skill and earning power, releasing a six-paragraph letter in which the unbeaten five-division champion said he no longer feels the passion that propelled him to the top of the family business.

Mayweather, a 31-year-old former Olympic bronze medalist, is calling it quits at the close of a remarkable 18-month stretch in which he beat Oscar De La Hoya and Ricky Hatton, made more than $50 million in the ring and became a bankable celebrity outside it.

"This decision was not an easy one for me to make, as boxing is all I have done since I was a child," said Mayweather, the son and nephew of three former fighters who all became top trainers. "However, these past few years have been extremely difficult for me to find the desire and joy to continue in the sport."

The WBC welterweight champ (39-0, 25 KOs) hasn't fought since knocking out Hatton last December, but was widely expected to take on De La Hoya in September in a rematch of their May 2007 bout, the richest fight in boxing history. Instead, Mayweather's retirement clears De La Hoya's schedule and opens a vacancy at the top of boxing just when it's undergoing a revival built partly on Mayweather's brilliance and showmanship.

Mayweather also made less-convincing retirement announcements after each of his last three bouts, but his letter somberly described his reasons to "permanently retire from boxing."

"I loved competing and winning and also wanted to continue my career for the fans, knowing they were there for me and enjoyed watching me fight," Mayweather said. "However, after many sleepless nights and intense soul-searching, I realized I could no longer base my decision on anything but my own personal happiness, which I no longer could find."

Though Mayweather cashed two huge paychecks in 2007, he has lately seemed much more interested in fame than fighting. In the last few years, he evolved from the endearingly cocky "Pretty Boy" to the wealth-obsessed "Money May" who was estranged from his father, De La Hoya trainer Floyd Sr., and uninterested in all but the most lucrative bouts.

In the past year alone, Mayweather has appeared on "Dancing With the Stars," worked on his record label, served as the honorary starter at the Indianapolis 500 and entered the wrestling ring for a choreographed tussle with the 440-pound "Big Show" at WrestleMania in Orlando, winning what's currently his final fight with a set of brass knuckles.

"Floyd was a very talented fighter, no question about it, but he got to a particular point where it was just for the money," said Bob Arum, Mayweather's longtime promoter with Top Rank before the boxer began promoting his own career. "Which is all right, it's a professional sport, but there's nothing wrong with his decision. It's a rational decision."

Though fans and promoters have clamored for Mayweather to take on unbeaten welterweight Miguel Cotto or another top competitor in perhaps boxing's deepest division, Mayweather had repeatedly dismissed the idea. Instead, he was in talks for another fight with De La Hoya, whose own career-ending plans will be altered.

"There comes a time when money doesn't matter," Mayweather said. "I just can't do it any more. I have found a peace with my decision that I have not felt in a long time."

De La Hoya had hoped to fight Mayweather and perhaps Cotto this year before turning full-time to his lucrative career in charge of Golden Boy Promotions.

"I am surprised a bit about the timing of it, but if he decides he wants to retire, that is his right," Golden Boy CEO Richard Schaefer told The Associated Press. "We did not announce that fight (between Mayweather and De La Hoya), so I can't really say that something fell apart. Floyd was certainly the name that we were focusing on for a September fight, so now we will go down the list and find, I'm sure, other names that will ensure a megafight."

Schaefer confirmed De La Hoya still intends to fight Sept. 20. Several welterweights will jockey for the chance to meet him in a guaranteed big payday, while every big name in boxing's middle weight classes from Hatton to Manny Pacquiao also could get in the mix.

Mayweather rose swiftly through the sport after his solid effort in the Atlanta Games. With peerless hand speed, superb athleticism and a grinning swagger, Mayweather won his first title at 130 pounds in October 1998, upsetting Genaro Hernandez.

He grabbed a lightweight crown in 2002 with back-to-back wins over Jose Luis Castillo, and he beat Arturo Gatti in June 2005 for the light welterweight title. Mayweather then won the IBF welterweight belt by beating Zab Judah in April 2006, and he added a light middleweight crown against De La Hoya last year.

"I am sorry I have to leave the sport at this time, knowing I still have my God-given abilities to succeed and future multi-million dollar paydays ahead, including the one right around the corner," Mayweather said.

Arum, who fostered Mayweather's development into a dominant champion before their acrimonious split, knows many fans still won't believe Mayweather is truly finished.

"You never know, but I will say the language was different this time," Arum said. "This time the language sounds like he might be done for good. ... I can hardly blame him (for retiring). We should commend him for what he's done. He's retiring at the height. Is there anything greater than that?"