The Outcasts were citizens of Taris that had been banished to the Undercity of the planet. They and their descendants were forced to live in dirt and filth, while having to beg for and steal food and clothes. The Outcasts lived in constant fear of the rakghouls—mutants which could spread their infection to anyone.
When new, smaller trade routes moved from Taris, rendering the planet unnecessary and without the support of the Republic, the planet began to fall into ruin and despair. The great city of Taris covered more than half the planet's surface, so the kelp harvest and the creatures of the sea were the only native food source.
Abandoned by the Republic, the Tarisian industrialists began to use certain power sources that would have been illegal under the jurisdiction of the Republic, which produced toxic waste as a byproduct. The pollution poisoned and killed most of the oceanic flora and fauna, leaving the planet with no reliable food source and beginning a famine. The Tarisian elite hoarded the remaining food and wealth for themselves, while the poor were left to starve and die.
The Tarisian poor rebelled, and began the Tarisian Civil War. Millions died, and large sections of Taris were destroyed or abandoned. The location of the only known self-sufficient part of Taris, known to the Tarisian poor as the "Promised Land," was lost. The rebellion was eventually crushed, and the thousands of remaining disarmed rebels were imprisoned. However, the jails were not large enough to hold them all, so instead they were banished to the Undercity, unable to return to the surface under penalty of death.
All hope was lost to the defeated rebels, save from one; the Promised Land. It was the hope that one day they might find the Promised Land that motivated the Outcast to carry on. In the meantime, Gendar's ancestor led the Outcasts to build the Outcast village in which they might survive that was by an elevator to the Lower City.
The prisons in the Upper City were rendered unnecessary, and any criminals in the Upper and Middle City were banished to the Undercity. Here, walking the original surface of the planet that never saw the sun due to the shadows of Taris' massive skyscrapers, they endured a lifetime of horror marked by starvation, rakghoul attacks and rakghoul infections. Even their descendants were forced to live in damnation. As the generations passed, fewer and fewer Outcasts believed in the tales of the Promised Land, thinking them to be fairy tales meant to prevent the Outcasts from going mad from despair.
In the year 4056 BBY, non-Humans were also banished and forced to live in the slums of the Lower City. Thus the law enforcement of the corrupt government enforced strict socioeconomic divisions upon the people of Taris for ninety years, from 4056 BBY until 3966 BBY. During this time Rukil's grandfather searched for clues about the Promised Land, but was killed by rakghouls in the Sewers. Rukil's father did the same and found more clues about its location, but he met the same fate.
When the Republic eventually dissolved the corrupt Tarisian government in 3966 BBY, the Outcasts' banishment was ended. However, Mandalorian attacks on Taris obstructed further efforts to emancipate the Outcasts. In 3964 BBY, the Republic reluctantly abandoned the planet to the Mandalorians and the Outcasts were once again forced to live in damnation. Even when the Mandalorians eventually withdrew from the planet in 3960 BBY, the Outcast's lives did not improve.
During the Jedi Civil War, in 3956 BBY, the Republic returned to the planet to finish the job they had begun during the Mandalorian Wars. In the Upper City, Republic scientists developed the rakghoul serum, a cure for the horrifying disease that plagued the Outcasts which was duplicated many times. The Republic was about to tighten the socioeconomic divisions once more when the Sith invaded.
During the Sith occupation, all followers of Rukil had abandoned him save from one, his apprentice called Malya. Rukil, who was too old to search for clues for the Promised Land, sent Malya to look for more. She indeed did find more clues, but she was killed by rakghouls in the Undercity surface before she could return to Rukil.
The Sith tightly controlled the use of the rakghoul serum, giving doses only to themselves and to their Undercity patrol. By the time Revan entered the Undercity, the Sith had practically run out of the serum altogether, though some of the Sith troopers killed by rakghouls would occasionally have a sample of serum on their corpses.
When Revan arrived at the Undercity, he saved the Outcasts from the rakghouls by giving a rakghoul serum vial (found on the remains of a Sith Trooper) to an Upper City doctor, Zelka Forn. Forn reproduced the serum and used it to cure the Outcasts of the disease, and Esala, the village healer, was given hundreds of vials from Zelka Forn. Revan also met Rukil and helped him discover the Promised Land. Revan found journals belonging to Rukil's grandfather, father and apprentice Malya in and around the city sewers. He then gave the tomes to Rukil, who in turn gave them to Gendar, who used them to discover the location of the Promised Land and led the Outcasts from their village.
The Outcasts survived the bombardment of Taris while traveling through the Tarisian sewers, where they found no survivors other than themselves, Gamorreans or otherwise. A few months after the bombardment, the Outcasts' exodus from their village to the subterranean realm known as the Promised Land was complete. It was discovered by a group of heroes during the Cold War that the Outcasts had in fact found the Promised Land; it was, however, vastly different from the legends, or at least was after the bombardment.
The buildings, equipment, generators and possibly droids had been destroyed, and therefore the Outcasts had to start over. Whilst being a difficult task, they had survived the bombardment. However, many generations had passed since then, each having a "Promised One," who would keep the memories of the terrible apocalypse and be in charge of the colonists.
The anti-rakghoul serum which Revan discovered was enough to protect the first few generations, but after the rakghouls evolved immunity to it, it was obvious the vials became useless and that babies couldn't be born immune and some rakghouls evolved into the Nekghouls. However, unlike the rakghouls, the Nekghouls couldn't spread infection.
The Outcasts later left the Promised Land and recolonized the Undercity and renamed themselves the Tarisians. This was in vain, however, as the Tarisians continued to die out on the surface from starvation, diseases and rakghoul attacks. It was also shown, in the last successfully preserved time recording, that the last generation alive had lost so much information about the world, they didn't even know how or what brought them there and the remaining members died out from toxic waste, which ultimately resulted in their extinction like the rest of the planet's population many years earlier. The information about them was lost until a Jedi retrieved the information about their post-apocalyptic history via hologram recordings both in the Promised Land and in the Undercity and gave it to a local Republic history keeper, in 3643 BBY.
The only legacy they left behind was a sample of a rakghoul serum, which was found by pirates in Zelka Forn's second medical facility, which was located in the Undercity in the remains of their village and was later given to a Jedi, although the Nekghouls were technically the descendants of the Outcasts. The Jedi group then gave it to a Republic scientist so someone could alter and improve the vial from someone infected so it wouldn't be useless. The deed was done and the serum was produced into mass quantities for a third time.
In an alternate, non-canon plotline, Revan gives the serum to one of Davik Kang's men for a large sum of money. In another non-canon plotline, Revan gave the three Promised Land journals to Igear, who destroyed them so that the Outcasts could never find the Promised Land.
In Star Wars: Knights of the Old Republic, all the Outcasts within the village are human, with the exception of those bitten by the rakghouls; however, the infected people were then quarantined away from the other members of the village.
- Star Wars Knights of the Old Republic: Prima's Official Strategy Guide
- Star Wars: Knights of the Old Republic Handbook