Koop severed under two U.S. Presidents, including the man who appointed him, Ronald Reagan.

Koop was the first Surgeon General to use the position as platform to speak out about health issues.

Koop is perhaps best known for his work on AIDS. He wrote a brochure about the disease that was sent to 107 million households in the United States in 1988. It was the largest public health mailing ever.

Prior to his appointment, Koop was surgeon-in-chief at the Children's Hospital of Philadelphia, where he was a pioneer in the field of pediatric surgery.

Koop was 96 years old.