Paul Allen, Microsoft Co-Founder
Allen -- with a net worth of $15 billion according to Forbes -- has donated more than $1.5 billion through the Paul G. Allen Family Foundation and direct contributions, including $26 million to Washington State University for its School of Global Animal Health.
He also established the Allen Institute for Brain Science with a donation of $500 million. The nonprofit focuses on advancing understanding of the human brain in health and disease.
In signing the Giving Pledge, Allen wrote, "My philanthropic efforts will continue after my lifetime. I’ve planned for many years now that the majority of my estate will be left to philanthropy."