Microsoft Corp co-founder Paul Allen, who had been suffering from non-Hodgkin’s lymphoma, a form of cancer, has died at the age of 65, his family says.

Earlier this month, Allen said he had started treatment for non-Hodgkin’s lymphoma, the same type of cancer he overcame nine years ago.

Born in Seattle, 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.

Allen, who left Microsoft in 1983, set up investment firm Vulcan Inc in 1986 to manage his multibillion-dollar portfolio.

“Paul Allen’s contributions to our company, our industry and to our community are indispensable,” Microsoft CEO Satya Nadella said in a statement.

“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.”

Google chief executive Sundar Pichai said “we lost a great technology pioneer today.”

“Thank you Paul Allen for your immense contributions to the world through your work and your philanthropy.”

Allen, who ranked 44 on Forbes magazine’s 2018 list of billionaires with a $US20.5 billion ($A28.7 billion) fortune, was a major benefactor in Seattle, funding everything from libraries and universities to brain research.

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.

“The raising of the “12th Man” flag at the start of every Seahawks home game was Paul’s tribute to the extraordinary fan base in the Seattle community,” NFL Commissioner Roder Goodell said.

“His passion for the game, combined with his quiet determination, led to a model organisation on and off the field… Our league is better for Paul Allen having been a part of it and the entire NFL sends its deepest condolences to Paul’s family and to the Seahawks organisation.”

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