Clifford Cox
Dr. Clifford Cox (played by Richard Beymer) was a plastic surgeon in Chicago in 1939, who was found to be using black magic and witchcraft to extend his life at the expense of his patients. Agents Mulder and Scully were brought in to investigate several gruesome deaths of patients at the hands of the Jack Franklin's doctors, a situation which Mulder believed to involve demonic possession. However, a nurse named Rebecca Waite was aware of Franklyn's true nature and attempted to kill him at his home.

Dr. Jack Franklyn

Cox posing as Dr. Jack Franklin

However, Franklyn fended her off and mysteriously filled her innards with nails. She coughed up the nails and was brought to the emergency room, and she died soon after. Mulder soon made the connection that Franklyn had been employed at the hospital many years earlier under a different name - and with a different
Dr. Hartman

Cox posing as Dr. Hartman

appearance. However, the agents were not fast enough to prevent a fourth patient's death, allowing Franklyn to complete his ritual of regeneration and escape. Franklyn vanished, but a highly qualified plastic surgeon under the name Dr. Hartman soon obtained a job at the City of Angels Medical Center in Los Angeles, California. (TXF: "Sanguinarium")