He continued, "With respect to Microsoft, stepping down from the board in no way means stepping away from the company. Microsoft will always be an important part of my life's work and I will continue to be engaged with Satya and the technical leadership to help shape the vision and achieve the company's ambitious goals."

In a statement, Nadella said "The board has benefited from Bill's leadership and vision. And Microsoft will continue to benefit from Bill's ongoing technical passion and advice to drive our products and services forward. I am grateful for Bill's friendship and look forward to continuing to work alongside him to realize our mission to empower every person and every organization on the planet to achieve more."

The move comes twenty years after he moved aside to make Steve Ballmer CEO, twelve years after he left a day-to-day role at the company, and six years after he last served as chairman of the board. When he left Microsoft in 2008 Gates cited his interest in public health, and the timing of this move certainly reflects his focus on trying to prepare for pandemics, as explained in a 2018 lecture. The Bill & Melinda Gates Foundation has publicly announced it's committing $100 million to the fight against COVID-19, including a collaboration with Wellcome and Mastercard that's funding an accelerator project for treatments.