4. Michael Dell (Chairman and CEO of Dell)

Estimated worth: $15.9 billion 

Estimated donations: $1.2 billion

Charity: Michael and Susan Dell Foundation 

In 1999, Michael and Susan Dell established the Michael and Susan Dell Foundation, which focuses on causes for children. By 2010, the foundation had donated more than $530 million to help nonprofit organizations serving urban communities in the United States and India.

The foundation has also provided $65 million in grants to three health-related organizations associated with the University of Texas: the Michael & Susan Dell Center for Advancement of Healthy Living, the Dell Pediatric Research Institute, and the Dell Children’s Medical Center, as well as funding for a new computer science building on the University of Texas campus. He also donated millions to the Hurricane Katrina relief fund.

In 2002, Dell received an honorary doctorate in Economic Science from the University of Limerick in honor of his investment in Ireland and the local community and for his support for educational initiatives.