Chris Collins, a vice president of amFAR, the Foundation for AIDS Research, said many people don't realize what an important role Koop played in the beginning of the AIDS epidemic.

NPR: Koop, Who Transformed Surgeon General Post, Dies

An assistant at Koop's Dartmouth College institute, Susan Wills, confirmed his death but didn't disclose its cause.

NPR: Koop, Who Transformed Surgeon General Post, Dies