"X" is the strange and mysterious man who informs and warns Mulder of some things. He has admitted to Mulder that he is afraid of getting killed like his predecessor, Deep Throat, and he won't risk his life for Mulder. "X" went head-to-head with Skinner after he had refused Scully's request for information on Mulder's whereabouts in "Endgame". One other time he took a more active role and stepped out of the shadows and intervened directly in Scully and Mulder's case, getting rid of a key figure from under Mulder's nose. After that, Mulder told "X" that he no longer wanted anything to do with him and "X" warned him that he was choosing a dangerous time to go it alone. Mulder was unsure of whose side "X" was on, it was later revealed that "X" worked for the Cigarette-Smoking Man, but that he may have his own agenda. Following his own agenda, "X" took pictures of a meeting between the Cigarette-Smoking Man and Mulder's Mother, however, the Cigarette-Smoking Man finds out about this and lays a trap for what he's learned is a leak in the organization. The trap was sprung and "X" was tricked into revealing his betrayal, which left him shot to death on Mulder's doorstep. With his last moments of life, "X" left a message for Mulder, SRSG, four initials that had led Mulder to a new player, Marita Covarrubias. With his death, "X" may have left more questions than answers.
