The See is not completed yet. Below is what has been established for the players in the game.
The See: They are a very large religious order tasked with operation and ownership of the majority of warp gates. Their fanaticism for their order is well known, with inquisitions formed to root out warp tainted people. With the control of the gates, the See are also the informal banking system used by most powers. They have a merchant caste that deals with all things money related.
Their military is the highest technology in the galaxy, utilizing the technological boost given to them by discovering and controlling the gates. They remain out of local conflicts, and even during the 5th Interstellar War they maintained neutrality and acted as the base of negotiations.
Any race can be part of the See, and they do not “own” any systems per se, but they do live on very large capital ships that move constantly in several “home fleets”.