5. Paul Allen (Co-Founder of Microsoft)

Estimated worth: $14.2 billion

Estimated donations: $1 billion

Charity: Paul G. Allen Family Foundation 

Paul Allen has made contributions to organizations related to health and human services, and toward the advancement of science and technology. Paul Allen had pledged $26 million to his alma mater, Washington State University, for its School for Global Animal Health. In the late 1980s, Allen donated US$18 million to build a new library at the University of Washington which was named after his father, Kenneth S. Allen. He also donated US$5 million in 2003 to establish the Faye G. Allen Center for Visual Arts, named after his mother.

With his sister, Jo Lynn Allen, Paul Allen pledged $100 million in 2003 to found the Allen Institute for Brain Science, a nonprofit corporation and medical research organization.

Paul Allen is also a founding member of The International SeaKeepers Society.

A report in February, 2012, named Allen as the most charitable living American in 2011.