Microsoft Co-Founder Paul Allen has died from complications of non-Hodgkin's lymphoma, Vulcan Inc. said Monday on behalf of his family.

Allen passed away Monday afternoon in Seattle at 65 years old, Vulcan said. His sister, Jody, said he 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. Paul's family and friends were blessed to experience his wit, warmth, his generosity and deep concern," she said in a statement. "For all the demands on his schedule, there was always time for family and friends. At this time of loss and grief for us – and so many others – we are profoundly grateful for the care and concern he demonstrated every day."

Through Vulcan, Allen's network of philanthropic efforts and organizations, the Microsoft co-founder supported research in artificial intelligence and new frontier technologies. The group also invested in Seattle's cultural institutions and the revitalization of parts of the city.

Vulcan CEO Bill Hilf said, "All of us who had the honor of working with Paul feel inexpressible loss today."

"He possessed a remarkable intellect and a passion to solve some of the world's most difficult problems, with the conviction that creative thinking and new approaches could make profound and lasting impact," Hilf said in a statement.

Earlier this month, Allen revealed that he had started treatment for non-Hodgkin's lymphoma, the same type of cancer he overcame nine years earlier. The Microsoft co-founder left when he was first diagnosed with the disease.

Current Microsoft CEO Satya Nadella said Allen made "indispensible" contributions to Microsoft and the technology industry. Nadella also said he learned a lot from Allen and will continue to be inspired by him.

"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," Nadella said in a statement.

Former Microsoft CEO Steve Ballmer called Alen a "truly wonderful, bright and inspiring person."

Steven Sinofsky, former president of Microsoft's Windows division, said Allen "did so much to shape lives with computing and his later work in science, community, and research."

Allen also ranked among the world's wealthiest individuals. As of Monday afternoon, he ranked 44th on Forbes' 2018 list of billionaires with an estimated net worth of more than $20 billion. He was also the owner of the NBA's Portland Trail Blazers, the NFL's Seattle Seahawks and had a stake in Seattle's Sounders soccer team.

This story is developing. Please check back for updates.

— CNBC's Matt Rosoff, Ryan Ruggiero and Reuters contributed to this report.

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