An X in the window is how Mulder contacts X. He usually comes to Mulder's apartment. In "Fresh Bones" X sent Mulder a cryptic message on a playing card telling him where to meet. The first time he called Mulder was in "The Host" telling Mulder that "he has a friend in the FBI".
In "Nisei" and "731" he tells Scully to stop Mulder from getting on the train, but at the end he is there at the end to kill the assasin and to rescue Mulder. "Wetwired" sees him playing even a more dangerous game using Mulder and other agents as pawns, though it is revealed that he worked under The Cigarette Smoking Man, but may have his own agenda.
Following a mysterious agenda in "Talitha Cumi" he spies on Mulder's mother and CSM, taking pictures of their meeting. To get the alien ice pick he savagely beets up Mulder. When Mulder manages to walk away, there are signs that X is getting fed up of their relationship. Unknown to X, CSM finds out about the pictures and lays a trap for what he has learned is a leak in their organization. The trap is sprung in "Herrenvolk" when the Consortium elders are led to Mulder's apartment by X. X is left shot dead on Mulder's door step, with him scrawling his last message with his own blood "SRSG" four initials that lead Mulder to a new player in the game Marita Covarrubias. Apparently X left more questions than answers for Mulder.
Appearance
A large black man. Like all these conspiracy types, he always wears a suit. He seems much more dangerous than Deep Throat.
Background
Not known. Probably military, judging by the fact that alot of his information is about the military. He seems to be at a lower level of the conspiracy than Deep Throat. While DT and Cancerman were equals, X seems to be a subordinate.
Relationship with Deep Throat
He calls Deep Throat his "predecessor" and seems to be acting partly out of loyalty to him. However, he says that he has no intention of going the same way as Deep Throat and dying for Mulder.
Episodes
"The Host" - calls Mulder and tells him he has a friend in the FBI.
"Sleepless" - "Who I am is irrelevant," he says. "I don't want to be here." He gives Mulder top secret information on sleep eradication experiments, designed to build a better soldier. Mulder asks how he can contact X again. "You can't" says X. "Closing the X-Files - separating you and Scully - was only the beginning. The truth is still out there, but it's never been more dangerous. The man we both knew paid for that information with his life - a sacrifice I'm not willing to make."
"Ascension" - He meets Mulder at Senator Matheson's offices and tells him that the senator can't help him, not without committing political suicide. "They have something on everyone," he says "The question is when they'll use it. No-one can help you now. Your channels of recourse and appeal are closed." Mulder accuses him of knowing what has happened to Scully, but X says, "this reaches beyond any of us, Mr Mulder - even my predecessor. Why kill Duane Barry if there was nothing to hide?" "You mean the government?" Mulder asks. "There are no answers for you, Mr Mulder," X tells him. "They only have one policy: Deny Everything."
"One Breath" - A desperate X holds Mulder at gunpoint and tells him to back off. "You got him killed!" X says, talking about Deep Throat. "You got her killed! That's not going to happen to me. You're my tool, you understand? I come to you when I need you. Right now you're heading in a direction that can lead them right here." When Mulder says he can't leave Scully, X says scornfully that he's a school boy. "I used to be you," X says. "I was where you are now. But you're not me, Mulder. I don't think you have the heart. Walk away. Grieve for Scully and then never look back. You will be able to live with yourself, Mulder."
He then coldly assassinates the man who took Scully's blood, saying that this is what it takes to get the truth. Later in the same episode he arranges to Mulder to kill the men who are coming to trash his apartment. He says that, after this, it would be best if they don't see each other again.
"Fresh Bones" - X summons Mulder to tell him something not very exciting about the military in Haiti. It's not even conspiracy related. Maybe it's just an attempt to re-establish contact after the rift on "One Breath." "I'd assumed our last contact would be our last," says Mulder, referring to that episode.
 "End Game" - X appears only at the end when Mulder requests a meeting, anxious to know where he can find the Bounty Hunter. X tells him, but warns him not to go. This episode is also the first in which we see the X in the window. Scully later uses this too and this is able to see X herself, though he refuses to help her and pretends he has come to the wrong room. Only a bloody fight with Skinner persuades X to tell Scully where Mulder is. As the fight ended with X holding Skinner at gunpoint, we can only assume that Skinner managed to appeal to his consience.
"Soft Light" - X says he knows nothing about the case, thus tricking Mulder into telling him everything. "I can't help you," he says, when Mulder's finished. "The last time I helped you I bloodied my fist and regrettably exposed my identity to associates of yours," he says, referring to End Game. Mulder promises him that he can trust Scully and Skinner like he can trust him, but X ominously tells him that "dead men can't keep promises. The next time the blood and regret could be yours. I'm not at your beck and call, Agent Mulder. I have nothing to gain and everything to lose by helping you." He tells Mulder not to contact him again.
Later we see that he is in fact working on the other side in this one as he is in charge of the men who come to kidnap Banton and steal his knowledge. When Mulder expresses his outrage at this, X says he over-estimates his own role in this relationship. He exists for X to use, not vice versa. Despite his loyalty to his "predecessor" (Deep Throat), he says, he's never made Mulder any promises. Mulder walks off in disgust. "We're finished," he tells X. "You're choosing a dangerous time to go it alone," X shouts after him.
"Anasazi" trilogy - Mulder calls for X but he doesn't come.
; "Nisei" and "731" - He appears, rather desperate, and tells Scully to stop Mulder getting on the train. he diesn't give much information, but he is clearly following the location of the train for he is there at the end to kill the assassin and rescue Mulder. While doing this he looks with interest at the alien hybrid, almost as if he's not seen one before, and seems to wish he had the time to save it too.
"Wetwired" - X, through a subordinate, gets Mulder started on the case. However, if what he says is true, he is also being watched closely by his own superior, who seems to be no other than Cancerman. Cancerman seems to have sent X to all the evidence of the experiment, now that its security has been compromised. He moved deliberately slowly, hoping Mulder would get there first (or so he says). Mulder accuses X of being a coward, hiding in the shadows and feeding him scraps of information. "You made me risk my life, risk my partners life and you never risk your own". When Mulder pulls a gun on X, X just smiles, saying "Truth is, you need me Agent Mulder".
At the end, X tells Cancerman the the security leak has been dealt with, while the identity of the informant is unknown.
"Talitha Cumi" and "Herrenvolk" - X spies on Mrs Mulder and Cancerman, taking photos. It is his phone call that gets Mrs Mulder to the hospital after her stroke. In "Talitha Cumi" his main concern seems to be to get the alien ice pick. He beats Mulder up savagely in an attempt to do this. Mulder manages to walk away, and there are signs that X is getting fed up with this relationship. "I ought to shoot you anyway, after everything I've given you," he says.
In "Herrenvolk", he is caught in a trap. The Consortium elders, aware that there is a leak, plant some false information and watch how it travels. This leads them to X, whom they then kill when he goes to Mulder's apartment. His last act is to scrawl "SRSG" in his own blood on the threshold.
"Unusual Suspects" (set in 1989) - X appears as the leader of a team of men who "sanitise" the warehouse full of secret experimental gas, and then cover-up the operation and get away before the police come. Later, he watches as Susanne Modeski is driven away at the end. When going about the cover-up (and unwittingly giving the Lone Gunmen their future name) he tells them that "on November 22, 1963 we got away with it. They say it was a Lone Gunmen" - and I rather like the use of we here. He also seems to have orders to keep on eye on Mulder even back then, since he tells the crew of men that "no one touches this man"
How Mulder contacts him
An X in the window - though how X sees it, we don't know. X usually comes to his apartment. In "Fresh Bones" X sent Mulder a cryptic message on a playing card, telling him where to meet.