First seen in "Sleepless," where he latches on to an investigation Mulder is conducting, the clean-cut, fresh-faced Agent Kycek at first looked like ayounger, less cynical version of Mulder himself. As time went on, however, he was revealed as a double agent, working for the Cigarette-Smoking Man to thwart Mulder's attempts to reopen the X Files. He materially contributed to Dana Scully's abduction by Duanne Barry and attempted to kill Mulder when Mulder went to rescue her.
Afterward he disappeared, only to resurface in "Anasazi," where he killed Mulder's father and framed Mulder for it. Mulder is now clearly aware of Krycek's involvment; indeed, the only way Scully could stop Mulder from killing Krycek was to shoot her own partner. Krycek escaped, only to reappear during a bungled assassination attempt on Agent Scully that resulted in the death of her own sister Melissa. That Mistake resulted in an attempt on Krycek's life. After a narrow escape, Krycek fled the country possessing a powerful trump card- a digital computer tape containing information on the government's involvement with and knowledge of extraterrestrial life.
