SAN FRANCISCO • Microsoft co-founder Paul Allen, who had been suffering from non-Hodgkin's lymphoma, has died at the age of 65, his family said.
Mr Allen died two weeks after publicly revealing that the cancer he fought into remission nine years ago had returned. The incurable cancer affects white blood cells.
He never married and had no children.
"My brother was a remarkable individual on every level. While most knew Paul Allen as a technologist and philanthropist, for us he was a much loved brother and uncle, and an exceptional friend," Mr Allen's sister Jody said in a statement announcing his death.
Born in Seattle, Mr Allen attended Washington State University for two years before dropping out to co-found Microsoft in 1975 with Bill Gates, a friend of his from high school.
A "heartbroken" Mr Gates remembered Mr Allen as "one of my oldest and dearest friends", adding: "Personal computing would not have existed without him."
"He was fond of saying, 'If it has the potential to do good, then we should do it.' That's the kind of person he was."
Mr Allen, who left Microsoft in 1983, set up the investment firm Vulcan Inc in 1986 to manage his multibillion-dollar portfolio.
"All of us who had the honour of working with Paul feel inexpressible loss today," said a statement by Vulcan.
Microsoft said Mr Allen's "contributions to our company, our industry and to our community are indispensable".
"As co-founder of Microsoft, in his own quiet and persistent way, he created magical products, experiences and institutions. And in doing so, he changed the world," added the company's CEO Satya Nadella.
Mr Allen ranked 44th on Forbes magazine's 2018 list of billionaires with a US$20.5 billion (S$28.2 billion) fortune.
While Mr Gates attended Harvard, Mr Allen studied at Washington State University and later invested heavily in research projects in his hometown of Seattle.
He invested US$100 million to found the Allen Institute for Brain Science in 2003. A decade later, he founded the Allen Institute for Artificial Intelligence to study the impacts on society of new technologies, and the Allen Institute for Cell Science to fund research for treatment of diseases.
His investments include ownership stakes in several professional sports teams, including the NBA's Portland Trail Blazers, NFL's Seattle Seahawks and Seattle Sounders FC of Major League Soccer.
"Paul Allen was the ultimate trail blazer - in business, philanthropy and in sports," said NBA commissioner Adam Silver. "As one of the longest-tenured owners in the NBA, Paul brought a sense of discovery and vision to every league matter large and small."
AGENCE FRANCE-PRESSE, REUTERS