The X-Files: 10 Best Characters Who Appeared After Season One
6. X
When Mulder and Scully first began their crusade for truth and justice, they were assisted by a deeply mysterious agent who called himself Deep Throat.
After Deep Throat's death at the end of season one, he was replaced by another agent who begrudgingly desired to help Mulder and Scully, this time going by a single letter, X.
X stayed on the show much longer than his counterpart and helped Mulder and Scully several times, though not without plenty of misgivings about the pair.
X would often switch from being incredibly helpful to incredibly shady, obviously trying to focus on saving his own neck than helping Mulder reach an easy end to his questions.
Mulder and X would often come into physical conflict often, especially whenever someone close to Mulder got injured, abducted, or killed. However, X ultimately decided to assist Mulder in uncovering the truth about the relationship between his mother and the Cigarette Smoking Man.
That case ended up being Mulder and X's final one, as X was revealed to be a traitor to the Cigarette Smoking Man's Syndicate, and was promptly executed in front of Mulder's apartment.
Even just before his death, and afterward, X still helped Mulder, showing he really did care more about the greater good than his life, a sacrifice Mulder never forgot.