Paul Allen, who co-founded Microsoft with his childhood friend Bill Gates, has died aged 65.

Mr Allen’s company Vulcan said in a statement that he died on Monday.

Earlier this month, Mr Allen said the cancer he was treated for in 2009, non-Hodgkin’s lymphoma, had returned.

Mr Allen, who was an avid sports fan, owned the Portland Trail Blazers and the Seattle Seahawks.

Bill Gates with Paul Allen in 2003
Bill Gates with Paul Allen in 2003 (Elaine Thompson/AP)

He and Mr Gates founded Microsoft in 1975 and the company’s big break came in 1980, when IBM decided to move into personal computers.

IBM asked Microsoft to provide the operating system.

The decision thrust Microsoft on to the throne of technology and the two Seattle natives became billionaires.

Both later dedicated themselves to philanthropy.

Over the course of several decades, Mr Allen gave more than two billion dollars to a wide range of interests, including ocean health, homelessness and advancing scientific research.