Paul Allen, who co-founded Microsoft with Bill Gates, died in Seattle on Monday. Allen’s investment firm Vulcan Inc announced that he died of complications from non-Hodgkin’s lymphoma, which is a cancer of the lymphatic system. He was 65.

“My brother was a remarkable individual on every level,” Allen’s sister, Jody Allen, said in a statement on behalf of his family. “He was a much loved brother and uncle, and an exceptional friend.”

On October 2, Allen tweeted that the non-Hodgkin’s lymphoma that he had treated in 2009 had returned and that he had begun treatment.

Allen founded Microsoft with Bill Gates in 1975, several years after the two met as students at a private school in Seattle, according to CNBC. He served as the company’s executive vice-president of research and new product development. Allen left the company in 1982 after he was diagnosed with Hodgkin’s disease.

Allen played a major role in developing the personal computer at a time when the typical computer was the size of a room and very expensive, according to The Guardian. Allen was also the one who came up with the name Microsoft.

He also bought two professional sports teams: the National Basketball Association’s Portland Trail Blazers and the National Football League’s Seattle Seahawks. He was involved with both teams until his death. He was an investor, entrepreneur and philanthropist.

“I am heartbroken by the passing of one of my oldest and dearest friends, Paul Allen,” said Gates in a statement on Monday, according to CNN. “Paul was a true partner and dear friend. Personal computing would not have existed without him.”

Chief Executive Officer of Microsoft Satya Nadella said Allen’s contribution to the company, the industry and the 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,” he said.

Google Chief Executive Officer Sundar Pichai thanked Allen for his contributions. “We lost a great technology pioneer today - thank you Paul Allen for your immense contributions to the world through your work and your philanthropy,” Pichai said.