Onderon, in the three-planet system of the same name, circles a yellow sun and has four moons with widely-varying orbits. The closest moon, Dxun, is home to numerous bloodthirsty creatures who are periodically able to migrate to the surface of Onderon, due to an annual period in which the two worlds' atmospheres intersect. The human inhabitants of Onderon gradually evolved defenses against the beasts, eventually culminating in the enormous walled city of Iziz. Native life on the planet includes the deadly dragon-bird.

4,400 years ago the Dark Jedi Freedon Nadd brought the power of the Sith to Onderon, and those who opposed it were cast out into the wilderness where they tamed the beasts of Dxun. Hundreds of these "beast riders" created their own kingdoms in the wild, and fought continually to overtake Iziz. About 4402 years ago Onderon was first contacted by the Old Republic, and a delegation of Jedi (including Ulic Qel- Droma) was sent to make peace between the beast riders and Queen Amanda of Iziz two years after that. Following the death of Queen Amanda, her daughter Galia took the throne with Oron Kira, her lover and the leader of a beast rider kingdom. A subsequent uprising by the followers of Freedon Nadd was put down by another Jedi force. At the same time, Satal Keto and his cousin Aleema (members of Tetan royalty) traveled to Onderon to learn the secrets of Sith magic, which led to their formation of the Krath and the political takeover of the Tetan system. Following the Naddist uprising, a permanent Jedi outpost was built on Onderon from the remains of Nadd's ancient starship. Later, during the end of the Sith War, Exar Kun ordered the warrior clans of Mandalore to capture Onderon and the city of Iziz. Defeated in a furious battle by Oron Kira and Captain Vanicus of the Republic navy, Mandalore and his surviving men fled to the Dxun moon. Millennia later, six years after the Battle of Endor, the Millennium Falcon landed on Onderon to repair damage suffered in a battle with the reborn Emperor's flagship, the Eclipse II. Fearing for her newborn son Anakin, Leia Organa Solo hid in warrior leader Modon Kira's safehouse deep in the Onderon wilderness. Palpatine (posing as a pilgrim on his way to the Shatoon monastery) discovered the child at the safehouse and tried to possess his body, but was stopped by the Jedi knight Empatojayos Brand. Later, the leaders of the New Republic gathered in the fortress of Modon Kira and re-established their galactic government, led by Mon Mothma with Leia Organa Solo as her second in command.