Renowned for leading the Smallpox Eradication Program, he later moves on to a prominent public health role and eventually aligns with Jahrling's research approach despite his initial reservations about smallpox stock destruction.

A dedicated USAMRIID researcher assisting Jahrling with smallpox studies, she transitions from a sports enthusiast to a passionate scientist while managing the demands of work and personal life.

A USAMRIID scientist known for his interest in bioreactors and training Hensley, he becomes embroiled in controversy over his credentials and security clearances, adding an element of uncertainty to his character.

A former high-ranking official in Russia's Biopreparat program who defected to the United States and demonstrates how easily bioweapons can be deployed, thus highlighting potential threats to civilian safety.

The pseudonym for the source of the Meschede smallpox outbreak, he is an electrician leading a hippie lifestyle, who likely contracted the disease during his travels in Asia, serving as an illustration of smallpox's impact.

A U.S. physician with a counter-cultural background who goes to India and plays a significant role in assisting D.A. Henderson with the eradication of smallpox, driven by his quest for enlightenment.