History
Gilgrath was a moon orbiting one of the planets on the edge of the Shi'ar Galaxy. Relatively recently it had become the home of one of the most cutting-edge scientific research facilities in the universe, with a staff made up of scientist from all over the galaxy working under Shi'ar protection.
Mentor was working on Gilgrath when his son Thanos confronted him to have him examine some illness that had afflicted him, in order to find a cure.[1]