This is well covered in many books and articles. The back story, as I understand, is that Allen was checked out from Microsoft even before he got sick. He was g

This is well covered in many books and articles. The back story, as I understand, is that Allen was checked out from Microsoft even before he got sick. He was going through relationship and other personal issues and went through long stretch of times travelling through Europe. Gates and Ballmer felt at the time that Allen received far bigger chunk of share of their success than he had actually worked for. You have to remember that Gates and Ballmer were both putting in 14-18 hours a day and many times not even have time to shower while Allen was touristing in Southern France for months with no indications of his commitments to the company. Even while at the founding of Microsoft, Allen's contributions to BASIC interpreter was not in balance as Gates but he did received same share of company because it was his idea. There are several authors who limit Allen's major contributions to Microsoft as: (1) Pointing out potential of microchips to Gates (2) be older face to partners like IBM (3) write small chunk of code in BASIC interpreter (4) suggest packaging apps as "office suit". There are few authors who believes that Allen did wanted to stay engaged but was sidelined by Gates when he started forming leadership team. This combined with his relationship issues and then sickness pushed him out of the loop. There are lot of parallels to Zuck and Eduardo except that Allen was lucky enough to be at right place and right time to overhear the plan to dilute his stack and prevent it before it was executed.