He was variously seen as either a henchman or enemy of the show's primary antagonist, The Smoking Man, changing his allegiance when the situation suited him best.

Krycek is a Russian-American, the son of Cold War immigrants,[1] who makes his first appearance in the season two episode "Sleepless", where as a young FBI Special Agent, he is assigned as a temporary investigation partner to Fox Mulder.

[4] Krycek also assaults Assistant Director Walter Skinner and acquires a secret tape from him which reveals a US government coverup regarding alien visits to Earth.

They learn that Krycek was recruited by an extremist militia group on a salvage hunt from the silo in North Dakota, and he informs the agents they must track the source of an extraterrestrial rock, brought to America by a foreign diplomat, to a gulag in Russia.

[6] Later in the series, Krycek can be seen switching sides as it suits him, occasionally helping Mulder, the Cigarette Smoking Man and other people.

[8] In the season seven finale, "Requiem", Krycek apparently kills the now wheelchair-using Cigarette Smoking Man by pushing him down a flight of stairs.

[11] Originally, the role of Krycek was offered to Callum Keith Rennie, who rejected it, but later made two guest appearances on the show.

[12] Krycek, who was initially created by writer Howard Gordon to temporarily replace Scully as Mulder's partner for three episodes, eventually grew into a character that lasted eight seasons on the show.