Ros Lai's father was a Jedi Knight in the last decades of the Galactic Republic. When he was sent to the planet Dathomir on a mission, this Jedi was captured by the Nightsisters and taken as a slave by the witch Zalem. As it was customary in the Dathomiri witches' culture, Zalem killed her husband after mating. Their daughter, Ros Lai, grew in the hate of her mother, and swore she would avenge the murder of a father she never knew.