Kurt Crawford (played by David Lovgren and by the Casey and Sean Murphy twins as children) was the name used by a series of hybrid clones produced from female abductees' ova.
Mulder met an adult series of these clones while looking for information about Scully's cancer. Half a dozen of them worked at the Lombard Research Facility developing other alien/humanhybrid clones like themselves. Like the other clone series, they could be killed with the alien gimlet weapon, and one of them was thus destroyed by the Syndicate's Grey-Haired Man. The Crawford clones provided Mulder and Scully with valuable information as they were part of the resistance and meant to subvert the colonization project.
The Kurt Crawford clones first appeared in the episode Herrenvolk as young Agrarian Drone boys, another part of this clone series. Mulder recognized the boys' face on one of the laboratory's developing clones, having first met them working along with his sister Samantha's clones on a farm in Alberta, Canada.