Paul Allen

Gates left his CEO position in 2000, handing the company reins to Steve Ballmer to devote more time to his charitable foundation

Allen's Stratolaunch had been compared to billionaire Richard Branson's Virgin Galactic

Despite always staying in the shadow of Gates -- his partner and friend since they were teenagers -- Allen was a passionate lover of computers and a key figure in the creation of Microsoft

Allen knew what he wanted and was ambitious about collecting

Allen died just two weeks after publicly revealing that the non-Hodgkin's lymphoma he fought into remission nine years ago had returned.

Microsoft said Allen's 'contributions to our company, our industry and to our community are indispensable'