Roger Mayweather, a two-time world champion who also found success as a trainer, died Tuesday after years of declining health and complications from diabetes. He was 58.

He was part of one of boxing's most famous families as the uncle of superstar Floyd Mayweather Jr., whom he trained for much of his career, and the brother of former pro fighters and trainers Floyd Mayweather Sr. and Jeff Mayweather.

"My uncle was one of the most important people in my life inside and outside of the ring," Floyd Mayweather Jr. said in a statement, just days after the death of Josie Harris, his former longtime girlfriend and the mother of three of his children. "Roger was a great champion and one of the best trainers in boxing. Unfortunately, his health was failing him for several years and now he can finally rest in peace.

"Roger meant the world to me, my father Floyd Sr., my uncle Jeff, our whole family, everyone in and around the Mayweather Boxing Gym and the entire boxing world. It is a terrible loss for all of us. We are thankful for all the love and well-wishes we have already received as word traveled about Roger's passing. It helps me to see that he was able to touch so many people through his life in boxing, because he gave so much to the sport which was his first and longtime love."

Roger Mayweather, a longtime Las Vegas resident originally from Grand Rapids, Michigan, boxed professionally from 1981 to 1999 and won world titles as a junior lightweight and junior welterweight. He faced many notable opponents during his 18-year career, including Julio Cesar Chavez Sr. (twice), Pernell Whitaker, Kostya Tszyu, Livingstone Bramble, Rafael Pineda, Vinny Pazienza, Rocky Lockridge and Samuel Serrano.

"This is a sad day for the Mayweather Promotions family because that is truly what Roger was to us," said Mayweather Promotions CEO Leonard Ellerbe, who worked side-by-side with Roger for many of Floyd's biggest fights. "On top of being a phenomenal fighter in his own career, Roger was one of the most essential parts of guiding Floyd to the incredible career he had in becoming the best ever. We hope you keep Floyd and the entire Mayweather family in your thoughts and prayers during this time."

In recent years, Roger's long boxing career filled with grueling fights seemed to catch up with him.

"He wasn't doing very well over the last couple of years," said former two-time world titleholder Jessie Vargas, whom Mayweather used to train. "I think it started back in 2010, 2011. That's when it was becoming obvious [that his health] was getting worse and worse. It was just tough for him to get over it. Over the years it became more difficult for him. The last time I saw him, it must've been about six months ago. He wasn't really visiting the gym as often because of his illness."

Mayweather (59-13, 35 KOs), known as the "Black Mamba," won his first world title in 1983, claiming the WBA junior lightweight belt by eighth-round knockout of Serrano.

Jesse Reid trained Mayweather for about eight years and for both of his title runs before they parted ways after his second loss to Chavez.

"The best fight with Roger was when he beat Sammy Serrano in Puerto Rico," Reid said. "He beat him in his backyard, just destroyed him. Roger, if he would've done road work, could've been a champion for a lot longer, but he was never a guy who liked to run. Then he started living a little high on the hog, and that caught up with him."

Mayweather made two successful defenses before losing the belt by first-round knockout to Lockridge in 1984.

In 1985, Mayweather challenged Chavez for his junior lightweight world title but was knocked out in the second round. In 1987, Mayweather faced another all-time great in Whitaker and lost a unanimous decision in a regional lightweight title bout. After that loss, Mayweather won his next two fights and landed a title shot against WBC junior welterweight world titlist Rene Arredondo and knocked him out in the sixth round to claim another belt.

Mayweather made four successful defenses before losing the title to Chavez in a rematch in 1989, a fight Chavez dominated before Mayweather retired on his stool following the 10th round.

Mayweather fought for junior welterweight world titles twice more but suffered a ninth-round knockout loss to Pineda for a vacant belt in 1991 and a one-sided decision challenging Tszyu in 1995.

"He was a real warrior," said Top Rank chairman Bob Arum, who promoted several of his fights. "He'd fight anybody. And even after he retired, he was a human voice in the Mayweather camp. With all the boasting and stuff that Floyd did, Roger was a reality check."

As Roger's boxing career was coming to an end, Floyd Jr. turned pro in 1996, and Roger served as his trainer while Floyd Sr. was incarcerated. Floyd Sr. eventually took over his son's training, but when father and son had a falling out, Roger -- who had his own falling out with his brother -- returned to lead Floyd Jr.'s corner in 2000. He trained Floyd Jr. for most of the rest of his career, until his health prevented it.

Roger was at the center of an infamous incident during Floyd Jr.'s challenge of junior welterweight world titlist Zab Judah in 2006 in Las Vegas. With five seconds left in the 10th round, Roger entered the ring because he was angry at Judah, who had fouled his nephew with a blatant low blow followed by a right hand to the back of the head.

As referee Richard Steele called timeout to give Floyd a chance to recover, Roger stormed toward Judah, which prompted Yoel Judah, Zab's father and trainer, to also enter the ring. He went straight for Roger and threw a punch, igniting a melee in the ring and a near-riot inside the Thomas & Mack Center.

Roger Mayweather was ejected from the fight, which Floyd Jr. went on to win by unanimous decision. The Nevada State Athletic Commission revoked Roger's trainer license for one year and fined him $200,000, which was his entire paycheck for training his nephew for the bout.

Roger also had legal issues outside the ring through the years, including a 2009 incident in which he allegedly attacked Melissa St. Vil, a female boxer he trained.

During the buildup to many of Floyd Jr.'s fights, Roger was a staple of the HBO reality series "24/7." Reid recalled one of the episodes fondly.

"I remember watching '24/7,' [and] he was training Floyd, and he said, 'The only white guy I respect is Jesse Reid,'" Reid said. "And when I saw that, I flew to Vegas and said, 'What the hell's going on with you, Roger? Are you changing or what?' He said, 'Yes, I learned a lot from you and just wanted to thank you.' I told him, 'God damn, that means a lot to me, to know that I helped you in some way.'"

Mayweather also had a sweet side, which Vargas recalled.

"I remember we were fighting in L.A., and we walked around a little bit after lunch. He saw someone on the sidewalk. He seemed like he was homeless, [and Roger] walked by and gave him $20 and kept walking," Vargas said. "He didn't even say anything to me about what he did. I just noticed it. He didn't think I had seen it, and he didn't even mention it. He did good things for people without having to brag about it. He just did it out of his heart. I know he was very outspoken, but he was also very generous.

"We all loved him for the person he was. We admired him as a fighter, a former world champion, a great fighter. Not too many people got too close to him that I did notice. He was good guy. It really hurts me, as it does the boxing world. The good thing is he'll no longer be suffering because I know his health, his condition wasn't very good. May he rest in peace without any suffering. A lot of us will miss him and love him."

ESPN's Steve Kim contributed to this report.