Bio: The man both foes and fans hate. Handsome, charming, and well-spoken, the treacherous Agent Alex Krycek (Nick Lea) worms his way into the confidence of Fox Mulder, first appearing in the second season episode Sleepless, where he plays a worshipful junior FBI agent sharing Mulder's passions and beliefs. He tries to get closer to Mulder trying to form a rift between him and Scully. But his true allegiance shows when he warns The Cigarette-Smoking Man that separating Mulder and Scully had not stopped their partnership, and that The Cigarette-Smoking Man has underestimated Agent Scully as a danger to their secrets.
His darker side appears even more clearly in the dual episodes Duane Barry and Ascension, where he is instrumental in the abduction of Agent Scully and the silencing of Duane Barry. His faithlessness earned him the moniker "Ratboy" from Internet fans.
His deceit exposed, he disappears from the Bureau, only to become a greater threat than ever as he goes underground. Acting almost as a hitman for the Consortium he bumps of both Mulder's father and Scully's sister. At the end of the second season, in Anasazi, he murders Mulder's father and frames him for the killing. Later in The Blessing Way he watched while his associate Luis Cardinal(with orders from the Consortium) fatally shot Scully's sister Melissa in the head mistaking her for Scully.
Since then, Krycek's motives have become somewhat fuzzy, and it seems as if he has had a falling out with the Consortium. In fact, they seem to have made a few unsuccessful attempts to get rid of him such as trying to kill him with a car bomb. He escapes with a digital audiotape (DAT) containing sensitive Defense Department files. Subsequently (Piper Maru) he was infected with the black oil (substance through which aliens can take control of people) and locked up by the Cancerman after he gives him the DAT tape. Since then his relationship vis-a-vis the Consortium and specifically Cancerman has deteriorated.
He now seems to be a free agent-double-crossing anybody and everybody. In Terma his ever shifting or rather non-existent loyalty again emerges when he becomes all-conspiratorial with the owners of a Siberian Gulag where he and Mulder are captured. His left arm was removed in a rather gross way in the same episode.
Ever the unpredictable, in cahoots with the Russians he then develops a vaccine at their Tunguska prison, which he uses as a bargaining tool with the Consortium in Patient X. In the same episode we learn of his alliance with Marita Covarrubias where we find that they have been partners in more ways than one. In true Krycek style though she double-crosses him.
In The End, he's back to doing the bidding of the Consortium…after exchanging a vaccine against the black oil developed by the Russians (The Red and The Black) in return for his freedom. Relations with the Cancerman though are still unclear…he has to stop himself from killing him in The End, yet later he is seen playing the perfect lackey to him (Two Fathers). At the same time however he is inciting Jeffrey Spender against his father. Subsequent developments have indicated that he is actually just using the Consortium as a front for his own agenda (One Son).
Meanwhile he has got himself a perfect weapon of leverage - he has A.D. Skinner under his control. Skinner had been injected with microscopic atom-sized machines which using nanotechnology could be programmed to kill him. Krycek controls these atoms and therefore Skinner. Skinner under this pressure hands over to him video tapes of his confidential discussions with Mulder and Scully. Alex goes on to kill Michael Kritschgau as well.

• Describing Scully to the Cigarette Smoking Man:
  "A problem. A much larger problem than you described." (Sleepless)

• Referring to the alien colonists, Krycek tells Mulder
  It's "a struggle for heaven and earth. Where there is one law: fight or die. And one rule: resist or serve."(The Red and the Black)

• "I don't appreciate being ditched like someone's bad date." (Sleepless)

• "The autopsy revealed 43 small internal haemorrhages and skeletal fragments which just doesn't just happen spontaneously, not without some kind of corresponding external trauma..." (Sleepless)

• "Where do you get off copping this attitude? I mean, you don't know the first thing about me." (Sleepless)

• "You know, back at the academy, some of the guys used to make fun of you." (Sleepless)

• "That would be me....Krycek.....Alex Krycek" (Duane Barry)

• "The truth, the truth... There is no truth. These men, they make it up as they go along. They're the engineers of the future." (Tunguska)

• "They found me in North Dakota. They liberated me on a salvage hunt... When you go underground you have to learn to live with the rats!" (Tunguska)

• "Tell them it's all going to hell...." (Patient X)

• "You tell them to kiss my american ass.." (Patient X)