Fox William Mulder was born on october 13, 1961 in Chilmark, MA, to William ja Tena Mulderille.

His fascination with the paranormal stems from a childhood incident - his sister Samantha disappeared from their home in Chilmark, Mass. (pop. 650) when he was 12 and she was 8. Mulder claims she was abducted by aliens; during regressions he recalled hearing his sister's cries for help, and a bright light which kept him paralyzed and told him that his sister would be all right. This memory differs from a dream Mulder experienced one night. He has vowed to continue his search for her.

Mulder was recruited into the Bureau after studying psychology at Oxford. He showed an inclination toward the off beat from the beginning of his career. Mulder chose "the basement office with no heat" where the FBI hides the X-Files. Only his network of contacts in Congress and other halls of power has allowed him to continue his investigations in the face of official indifference and covert opposition. Opposed by enemies within the Bureau itself and beyond, the only person he can trust absolutely is his partner, Dana Scully.

Mulder is known around the Bureau by the nickname of "Spooky" because of his interest in paranormal phenomena.