Mulder's most influential secret source was introduced in the second episode of the series, in which he suddenly appears to warn Mulder away from a case. He repeated similar warnings in his other appearances, while at the same time feeding Mulder information to help him with his investigations. Always cryptic, he readily admitted on one occasion to lying to his protege. He stepped in to save Mulder's job in "Fallen Angel," and in "The Erlenmeyer's Flask," he saved Mulder's life at the price of his own.
Deep Thraot, whose real name and affiliations were never revealed, was a man seemingly caught in the middle. While he claimed to have such a "lofty position" that he can't get Mulder's box seats in any baseball stadium in the country (a sign of real power), he also confessed that he put his life in jeopardy every time the two met. He claimed to have watched Mulder for a long time, assessing his fitness, before confiding secret information to him. While Mulder believed him implicitly from the beginning, Scully was more doubtful. It was not until she was forced into and alliance with him to save her partner's life that she brought herself to trust him.
There are a few hints about Deep Throat's background. He said he worked for the CIA in Vietnam and belongs to an organization which had been guilty of "heinous acts against man." It appeared to be his goal to bring down this organization, through the actions of Mulder and Scully. He had been able to obtain highly classified Top Secret documents and pass them to Mulder in a very short time. He had access to some excellent resources for disinformation, as his faked UFO photo in "E.B.E.," designed to lure Mulder and Scully away from a "hot" investigation, was almost good enough to fool an expert like Mulder.
Deep Throat's most remarkable revelation was in "E.B.E.," wherein he sais he was one of three men in the world to have not only seen but killed an alien. He detailed for Mulder the setup of an international conspiracy devoted to the capture and execution of extraterrestrial visitors. In fact, so shattering was that experience, that Deep Throat confessed he had embarked on this mission of bringing information to Mulder as a form of penance. Yet Mulder found this hard to believe, as his deep faith in his informant was shaken by lies and misdirection.
From his hint to Mulder in his first appearance ("They have been here for a very, very long time.") to his dying words ("Trust no one!"), his influence on Mulder and on the X Files has been profound.
