They're a clone race, duplicating themselves from human originals (such as Mulder's missing sister), and are working on a variety of projects - mostly inventing ways of making humanity resistant to infection from the Black Oil, but also looking at destroying alien abductees useful to the colonising aliens.

Their main fear are the colonising aliens, who send shape shifting alien bounty hunters to kill them. An alien clone can be killed with a distinctive sharp object stuck into the neck. If their skin is punctured, the clones release a chemical that is toxic to humans. The clones have, on occasion, tried to enlist Mulder's help. On one occasion they sent a clone of his sister to him - a plan which backfired rather badly.