Dr. Appollinaire is the nineteenth-century San Francisco physician whose cholera ward becomes a hunting ground for the Devidians, and who grows suspicious of the Enterprise officers working there in Time's Arrow, Part II.
Dr. Appollinaire appears in Time's Arrow, Part II, the opening episode of the sixth season. He is a doctor at an infirmary in San Francisco in 1893, where a cholera outbreak is filling the wards with the dying.
The outbreak is providing cover for the Devidians, who are draining the neural energy of patients, and so the stranded Enterprise officers place themselves in the hospital. Beverly Crusher works on the ward as a nurse while the others pose as staff and investigators. Appollinaire is baffled by deaths that do not fit the disease and by a nurse who seems to know more medicine than he does.
When the officers confront a pair of disguised Devidians in the ward and seize their cane-like device, the doctor is left amid the confusion as the police arrive and the strangers flee.