Forerunner
From Halopedia, the Halo wiki
Summary
The "Forerunners" is the translated Covenant name for the race that built The Halos. It is theorized that this same race is responsible for the artifact that was found on Reach, and on Sigma Octanus IV.
The artifacts appear to have originated on different worlds, but have somehow made it onto these other planets. These artifacts are our only means of finding information about the Forerunner.
In Halo 2, 343 Guilty Spark explains that after exhausting every other strategic option, the Forerunners destroyed themselves along with other sentient life three radii of the galactic center by activating the Halos.
