Casti Tholon was a scout who grew up among the Duros and was Human by birth. She also worked as a staff member at the Galactic Outdoor Survival School.
Casti Tholon, originally from Sardoran, spent her childhood on Duro, in one of the Duro space cities, being raised by Duros as a foster child. She was only familiar with Duros and their traditions as a child, and she even thought of herself as a Duros, not a Human. However, she was argumentative and bossy, unlike most Duros, and she frequently took charge.
Casti Tholon, a born scout, was employed by Rim Commercial Mining to find and map planets located in Wild Space and the Unknown Regions. The first planet she found, which was also the most significant, was given the name Tholon in her honor.
While traveling through the Kur forests, she was wounded and poisoned by thorny vines that scratched her lower legs and arms, resulting in black scars. She also had scars on her head, which were always visible because she always kept her head shaved.
She was once a student at the Galactic Outdoor Survival School, and she later became a member of the School's staff. She was dedicated to her job and devoted to Barosa Warren, her employer and close companion. Everyone knew that Warren disliked former students who had joined the Rebellion. Tholon was apparently politically neutral, but her devotion to Warren made ex-alumni and Rebel officer Major Sisquoc see her as a serious threat to him and his team.