Best known for co-authoring the Bell-Lapadula Model with Len LaPadula

Wikipedia entry for Bell-LaPadula Model: http://en.wikipedia.org/wiki/Bell%E2%80%93LaPadula_model

Oral History at the Babbage Institute: http://conservancy.umn.edu/handle/11299/144024

Internet Archive of Dr. Bell's personal website: https://web.archive.org/web/20120503204522/http://star-property.offthisweek.com/

Inducted into the (US) National Cyber Security Hall of Fame 2013 http://www.cybersecurityhalloffame.com/

From the Cyber Security Hall of Fame page:

"Co-author of the Bell-LaPadula model of computer security"

"Dr. Bell was the co-author of the Bell-LaPadula model of computer security (with Leonard J. LaPadula). The model became the most widely used security model in the development of trusted (secure) computer systems. 

"His two papers “Lattices, Policies and Implementations” and “Putting Policy Commonalities to Work” showed not only that any Boolean policy could be supported by any Boolean-policy implementation, but also that every “different” security policy in the literature was a Boolean security policy, and hence supportable by any Boolean implementation."