Rattatak was a barbaric place. It's entire cutlure revolved around The Cauldron, a gladitorial arena. Jedi Knight Ky Narec crashed there shortly before the Clone Wars. She discovered Asajj Ventress there and trained her as a Jedi. The two of them tried to bring peace to the planet, but that worked out about as well as could be expected for a planet centered on gladiatorial combat. The people rose up and killed Narec, but Ventress went nuts and ended up taking over the planet on her own.
Ventress is really the only known Rattatakan.