Coming late to basketball, he nevertheless found stardom, retiring with the second-most blocked shots in league history. He devoted much of his life to humanitarian causes.

Dikembe Mutombo, who arrived at Georgetown University as an international student with aspirations of being a doctor but who instead became a towering presence in professional basketball and a dedicated humanitarian in his native Democratic Republic of the Congo, died on Monday in Atlanta. He was 58.

The cause was brain cancer, according to a statement by the National Basketball Association. His family announced in 2022 that he was undergoing treatment for a brain tumor in Atlanta.

Mutombo did not play basketball until midadolescence, having preferred soccer as a child. An older brother, Ilo, and his father, Samuel, encouraged him to try the sport in which his outsize frame, which ultimately stretched to 7 feet 2 inches, combined with his athletic agility, could be of greater benefit.

He wound up playing 18 seasons in the N.B.A. for six teams, retiring with the second-most blocked shots in league history behind Hakeem Olajuwon, another African-born center. Mutombo was known for his trademark finger wag, a provocative pose he used to dissuade shooters from challenging him at the rim.

At 21, Mutombo enrolled at Georgetown in 1987 on an academic scholarship after Herman Henning, an administrator at the United States Embassy in Kinshasa, the Republic of the Congo’s capital and a former high school basketball coach, sent word of him to John Thompson, coach of the vaunted Georgetown program.

After playing only intramural basketball during freshman year while gaining fluency in English, Mutombo abandoned pre-med courses, a concession to the demands of major college basketball. He switched to a double major in linguistics and diplomacy. He spoke French, English, Spanish, Portuguese and five African languages.

Though his basketball skills were initially raw, Mutombo trained during summers with Patrick Ewing, a Georgetown alumnus and N.B.A. All Star center, and a teammate, Alonzo Mourning, another center and budding N.B.A. star. By his senior season, Mutombo averaged 15.2 points, 12.2 rebounds and 4.7 blocked shots per game.

“Basketball-wise, he’s just a babe in the woods,” Thompson told The Washington Post in 1991. “He hasn’t been brought up being given things and being told how great he is, and he wants to get better.”

Selected fourth in the 1991 N.B.A. draft by the Denver Nuggets, Mutombo was immediately intimidating on defense. Though awkward-looking, he had an effective hook shot, which helped him average what would be a career-high in points, 16.6. He made the first of eight All-Star Game appearances.

The highlight of Mutombo’s five years in Denver came when he anchored the Nuggets’ upset of the Seattle SuperSonics in the first round of the Western Conference playoffs in 1994. In the decisive fifth game, after grabbing the final rebound in overtime, he was memorably photographed lying on the court holding the ball aloft, celebrating the first-ever defeat of a first-seeded team by one seeded eighth. (The Nuggets were eliminated in the second round by the Utah Jazz.)

Mutombo moved on from Denver in 1996, signing a five-year, $55 million contract with the Atlanta Hawks. Pete Babcock, the Hawks’ general manager, said in a 2022 interview for this obituary that Mutombo had been intrigued by Atlanta as a base for a foundation that he envisioned establishing for the benefit of his home country, then colloquially known as Zaire. He started the foundation in 1997.

“When we recruited Dikembe, we tried to impress upon him how diverse Atlanta was, how important the African-American community was compared to most large American cities,” Babcock said. “That first summer we signed him, he was buying school buses and shipping them to the Congo, and talking about how unstable the country was due to civil strife, especially the medical facilities.”

Mutombo’s mother, Biamba Marie, died at home in 1998 after having a stroke; he had been unable to get hospital care for her due to a government-enforced curfew. That year, he invited business and political insiders to a dinner in Washington to announce a fund-raising campaign for a hospital in Kinshasa to provide treatment for the poor. Over the next several years, he struggled to raise money, even from people within the N.B.A., two notable exceptions being Ewing and Mourning.

“I thought it would be easy, that I would call up all the rich people I knew from being a basketball player and the whole thing would take nine months,” he told The New York Times weeks before the 300-bed hospital, named for his mother, opened in September 2006, on land donated by the government. He said that he had to pay squatters to vacate the property and that he had donated roughly $15 million to the project.

“This is going to be the proudest day of my life,” he said during the ceremonial opening.

As a basketball player, Mutombo could be idiosyncratic, even churlish, especially when compared to his Georgetown brethren Ewing and Mourning. Though he was voted Defensive Player of the Year four times by the news media, he at times complained of being underappreciated.

“Wanting people to recognize his accomplishments, in a sense, is a certain type of pride that’s part cultural,” Mutombo’s cousin Dr. Louis Kanda, a Washington surgeon whose career path Mutombo initially hoped to follow, told The Washington Post in 1995.

His finger wag popularized him, along with his gravelly voiced, thickly accented proclamations, typically followed by deep-throated laughter. Reporters delighted in his misadventures with Americanized expressions — he once described Shaquille O’Neal’s playoff opposition as “a walk in the cake.”