Rubicun III was the inhabited third planet of the Rubicun system, which was located in a star cluster. Classified as M class, this was the homeworld for the Edo, a pre-warp capable humanoid species.
The Edo were protected by a trans-dimensional being who they worshiped as their God. Random punishment zones were moved around on the planet's surface.
The USS Enterprise-D visited this planet after delivering Earth colonists to the neighboring Strnad system. (TNG: "Justice")