Rattatak was an Outer Rim world unknown to the Galactic Republic at the time of the Clone Wars.
Rattatak was a dry, arid, mountainous planet covered in red rock, judging by its appearance from orbit. Most settlements appeared to be hewn into the rock itself. Rattatak's climate was too harsh to sustain widespread agriculture.
Rattatak was one of the unexplored planets in the galaxy. Isolated, the Rattataki fought each other as well as at least one other sentient species in never ending battles. Their way of fighting evolved over the centuries, ranging from melee weapons to blasters. A couple of warlords, the Ventresses, massed an army in the southern hemisphere. Osika Kirske killed the two; only their foster daughter, the young Nightsister Asajj, escaped.
Soon, a "warlock" fell from the sky, claiming to be an emissary of the Galactic Republic. On sight, they attempted to kill him, but he escaped and found Asajj. Finding that she was strong in the Force, he began training her as his Padawan. Together they united armies and brought peace to the planet. Unfortunately, the warlords feared them and united together to kill the pair; they only killed the master. In her rage, Asajj captured and/or killed every warlord responsible for her master's death and established a totalitarian regime over the planet.
Most of the planet was subjugated by the Stunger state
It was here that Count Dooku first discovered and recruited Asajj as he watched her emerge victorious at the gladiatorial death matches of The Cauldron. He introduced her to Darth Sidious who gave the dark side warrior her first assignment, which was to kill Anakin Skywalker, only to test the boy on whether he would be the perfect Sith apprentice. Later in the Clone Wars, Obi-Wan Kenobi was transported to Rattatak by Asajj after her victory on Jabiim.