Mysterious creatures of unknown origin, the mimetic aliens once traveled to the S.G.C. and managed to take control of the entire facility, after abducting an SG team off-world and using their technology to make themselves appear as the team, in order to infiltrate Earth. Very little is known of the species, but it is reasonable to assume that their goal was to take control of the United States government, and eventually the entire planet.
The species' physical appearance is unknown as well, as they appear to be encased within an exoskeleton or armor of sorts. Their language is no less alien, sounding more like a collection of guttural grunts than articulated syllables.
The mimetic aliens gain their names from the advanced technology they possess: a machine capable of processing a person's physical body and programming his or her appearance into a wearable device the aliens use to "mimic" the appearance of the individual. They also possess the technology to access the subject's memories; one device remains attached to the unconscious subject's head, while another is placed on the temple of the alien impostor.
Fortunately, the mimetic aliens' plot was unraveled due to a collaborative effort from SG-1 and Colonel Harold Maybourne. But before a number of creatures escaped, they demolished the S.G.C. gate room by self-destructing. It is unclear as to what their long-term plan was in controlling the S.G.C., but one can suspect sinister purposes behind the infiltration.
HOMEWORLD - Unknown
FIRST APPEARED - Foothold
Foothold - SG-1 returns from a mission to find that the base has been compromised by an alien force that is rapidly replacing personnel with alien duplicates.