The Unknown alien race is an unknown species from the Milky Way galaxy. Considering the level of technology the Gadmeer had reached, this species must have been at least as advanced as them, having been able to defeat the Gadmeer. It is speculated that the unknown alien race is the Goa'uld.
History[]
They made contact with the Gadmeer at an unknown time when they attacked the planet. These aliens were never seen on screen. (SG1: "Scorched Earth")