Dikembe Mutombo, the Hall of Fame, finger-wagging center who spent much of his post-basketball career as an ambassador for the sport, died of brain cancer at the age of 58, the NBA announced Monday.

Mutombo's family revealed two years ago he was undergoing treatment in Atlanta for a brain tumor. The NBA said he died surrounded by his family.

"Dikembe Mutombo was simply larger than life," NBA commissioner Adam Silver said in a statement. "On the court, he was one of the greatest shot blockers and defensive players in the history of the NBA. Off the floor, he poured his heart and soul into helping others.

"There was nobody more qualified than Dikembe to serve as the NBA's first Global Ambassador. He was a humanitarian at his core. He loved what the game of basketball could do to make a positive impact on communities, especially in his native Democratic Republic of the Congo and across the continent of Africa. I had the privilege of traveling the world with Dikembe and seeing first-hand how his generosity and compassion uplifted people. He was always accessible at NBA events over the years -- with his infectious smile, deep booming voice and signature finger wag that endeared him to basketball fans of every generation."

Mutombo played 18 NBA seasons for the Denver Nuggets, Atlanta Hawks, Philadelphia 76ers, then-New Jersey Nets, New York Knicks and Houston Rockets before retiring after the 2008-09 season.

The 7-foot-2 former Georgetown center was the league's top defensive player four times, earned three All-NBA selections and played in eight All-Star Games. He ranks 20th in rebounds (12,359) and finished with 3,289 blocks, second to Hakeem Olajuwon (3,830).

"It's a sad day, especially for us Africans -- and really the whole world -- because, other than what he's accomplished on the basketball court, I think he was even better off the court," Philadelphia 76ers center Joel Embiid, who was born in Cameroon, said Monday. "He's one of the guys that I look up to, as far as having an impact, not just on the court but off the court. He's done a lot of great things. He did a lot of great things for a lot of people, so he was a role model of mine. It's a sad day."

Mutombo also was part of one of the league's most iconic playoff moments, helping eighth-seeded Denver oust top-seeded Seattle in the first round of the 1994 Western Conference playoffs. That best-of-five series marked the first time in NBA history a No. 8 beat a No. 1.

"As a basketball player, he might have been the best defensive player to ever play the NBA," former Nuggets coach Dan Issel said. "I never saw [Bill] Russell playing, but he'd have to be awfully good to be as good as Dikembe. You're very fortunate as a coach when your best player is the one that works the hardest and keeps all the rules, which is what Dikembe did. But his legacy might be even bigger with the work that he did off of the court."

Mutombo was inducted into the Basketball Hall of Fame in 2015 after averaging 9.8 points and 10.3 rebounds for his career. His No. 55 jersey is retired by the Nuggets and the Hawks.

"Like many across the globe, my heart is heavy with the loss of Atlanta Hawks legend and humanitarian Dikembe Mutombo," Atlanta Mayor Andre Dickens said. "I am grateful for the opportunity to visit with him and his wife, Rose, at their home last month and express the gratitude and pride Atlantans and millions worldwide held for such a truly good man. He is not just a Hall of Famer -- he is irreplaceable."

Said Milwaukee Bucks star Giannis Antetokounmpo: "He was always there to talk to me and advise me on how to approach the season and take care of my body and icing after games and stretching and trying different things like yoga. He will be always remembered, and may his soul rest in peace."

Mutombo followed most blocks with a playful wag of his right index finger, a gesture that became his enduring signature and inspired many others after him.

"Any time I would block shots, people would still be coming and trying to put a little bit on me. Then I used to shake my head every time I would block the shot," Mutombo once explained. "Then I said, man, f--- this. Those guys are not listening to me. Maybe if I start giving them the finger wag. And I tell you what, I lost a lot of money because of that finger wag, man. I got so many technical fouls, but no referee would kick me out of the game."

After his playing career, Mutombo worked extensively for charitable and humanitarian causes. He served as an ambassador for the sport, particularly in the development of the Basketball Africa League.

"It's really hard to believe, and it's hard for us to be without that guy," tearful Toronto Raptors president Masai Ujiri said. "You have no idea what Dikembe Mutombo meant to me. ... I have to say, though, that guy, he made us who we are. That guy is a giant. An incredible person. Who are we without Dikembe Mutombo? Not possible. It really is not.

"I went to Dikembe Mutombo's hometown with him. I went to his hospital, and you have no idea what that guy means to the world. He's gone. He's left us. ... That guy was the biggest giant that you could ever find. The biggest heart."

Sixers president Daryl Morey, who was with Mutombo for many seasons in Houston, was informed of his friend's death during the team's media day Monday. Tears welled in Morey's eyes as he processed the news.

"There aren't many guys like him," Morey said. "Just a great human being. When I was a rookie GM in this league, my first chance in Houston, he was someone I went to all the time. ... His accomplishments on the court, we don't need to talk about too much. Just an amazing human being, what he did off the court for Africa. Rest in peace, Dikembe."

Mutombo spoke nine languages and founded the Dikembe Mutombo Foundation in 1997, concentrating on improving health, education and quality of life for the people in Congo. His foundation led the building of a 170-bed hospital in Kinshasa, the capital city, and that facility has treated nearly half a million people regardless of their ability to pay for care.

And on occasion, LeBron James pointed out with a laugh Monday, Mutombo didn't necessarily improve the health of others.

"My fondest memory of Dikembe Mutombo? He fractured my face on my birthday in Cleveland with an elbow," James, the Los Angeles Lakers' star, said while taking several minutes Monday to pay tribute to Mutombo's life. "I never even got an opportunity to tell him about that. But yeah. I don't remember how old ... I was in Cleveland, my first stint, and I think I was turning 22 maybe?

"I went to the hole and caught one of those Dikembe elbows, and if anybody know about the Dikembe elbows, they do not feel good. He fractured my face, and I went to the hospital that night, and I wore a mask for a little bit. That is my memory of Dikembe."

Mutombo also had served on the boards of many organizations, including Special Olympics International, the CDC Foundation and the U.S. Fund for UNICEF.

"Dikembe's indomitable spirit continues on in those who he helped and inspired throughout his extraordinary life," Silver said in his statement. "I am one of the many people whose lives were touched by Dikembe's big heart and I will miss him dearly. On behalf of the entire NBA family, I send my deepest condolences to Dikembe's wife, Rose, and their children; his many friends; and the global basketball community which he truly loved and which loved him back."

Ryan Mutombo, the Hall of Famer's son, said in a tribute posted on social media that his father "loved others with every ounce of his being."

"My dad is my hero because he simply cared," Ryan Mutombo wrote. "He remains the purest heart I have ever known."

The Associated Press contributed to this report.