The planet originally known as Gelefil was an agricultural world between Ingo and Ko Vari. It was one of seven inhabited planets out of a total of fourteen in the Annoo system of the Tharin sector of the Outer Rim Territories. The main hyperspace route to the planet was the Nimat Corridor which route passed through the system. It was inhabited by the peaceful, long-lived Ret. The planet was later renamed Annoo after it was conquered by the Annoo-dat.
In about 322 BBY, the Annoo-dat of neighboring Annoo abandoned their dying homeworld and conquered Gelefil. Within a century, the Ret adopted Annoo-dat culture and they became a single civilization, both species referring to themselves as Annoo-dat and to Gelefil as Annoo. To distinguish between the two species, xenobiologists referred to the Ret as Annoo-dat Blue and the original Annoo-dat as Annoo-dat Prime, however the Annoo-dat did not use such terminology.
Agriculture on Annoo became highly industrialized on the southern continent (the northern continent remaining much as it always had) and the Tra'ang'a language of the Ret fell out of use, all Annoo-dat speaking Dat-an.
In about 27 BBY, General Ashaar Khorda attempted a bloody coup, but he was defeated by the Galactic Republic forcing him to go into hiding.
During the early years of the Galactic Empire, the notorious crime lord, Sise Fromm, had a stronghold on Annoo from where the Fromm Gang plotted the takeover of the other major gangs. At the same time, Demma Moll and her daughter, Kea, had a farm complex on the planet and formed a resistance cell in opposition to the Fromms and the Empire.