Conrad Strughold was one of the highest-ranking members of the Sydicate (aka "the Project") that involved the Cigarette-Smoking Man, the Well-Manicured Man, and others who chose to
collaborate with the alien colonists as a means of survival.
Strughold seems to be a German national and industrialist of some influence. He is likely the founder or heir of a mining conglomerate, the Strughold Mining Co., which plays a key role at one point in the show. The name "Strughold" is first introduced in the Season 3 episode "Paperclip", when Mulder and Scully visit the West Virginia operations of Strughold's company, where
files on US smallpox vaccine recipients are housed in old mining tunnels.
Strughold himself seems to remain strictly outside the US. We encounter him in the (first) X-Files film, where he
meets with other Syndicate members in London to assess the threat posed by the second generation of the black oil (which gestates a biological entity inside its host).
At the end of the film, he
is in Tunisia, supervising the expansion of the Syndicate's operations in agriculture and bee husbandry.
Given the rapid turn of events in the Season 6 episode "One Son", it is unlikely that Strughold travelled to the US to
meet his demise with the other Syndicate members at the airforce base. (Certainly, we do not see him amongst the group that is attacked by the alien rebels.)
I do not believe that Strughold is referred to again in the show.
Is there any information in extended media (interviews, novels, novelizations, comic books) regarding the fate of Conrad Strughold?
Pursuant to this, in Season 7, we see the Cigarette-Smoking Man's attempts to
rebuild the US side of the Syndicate, with Alex Krychek and Marita Covarrubias in assistance. As part of this, we learn that Alex Krychek had been captured in Tunisia, after his divergence from the Syndicate in "One Son". Is there any evidence that he was working for (or against) Strughold prior to his detention? Given Strughold's resources and influence, the Smoking Man may have viewed him as a competitor, and sent Krychek overseas to undermine Strughold's operations. Is there any information out there regarding Krychek's time in Tunisia and possible interactions with Strughold?
Finally, what became of Strughold and his international arm of the Project after the
rise of the supersoldiers?