GAIA is not a single entitiy, but rather a collection of AIs. It is the controlling entity of Installation X, and has a similar job to that of Monitors. However, unlike them, he does not have a physical avatar. However, it could be said that the ring is his self, as he is connected to everything on the ring. He was put there to observe the ring, as well as keep track of the flood in the valley of the forerunners. He is quite powerful, he can use any system on the ring at a whim. Thankfully, it does not contain a library as it does not have a superweapon, and he is quite peaceful, prone to quietly observing but not interfering. Indeed, during the battle of Installation X, he did not want to act, but was conviced by Andrea and Michael Harrington. It is suspected that GAIA has it's own sinister purposes in mind for Installation X, but it is unknown what those purposes are.