Furball was a nexu of the female variety, who was under the ownership and training of a human inhabiting the planet of Ruusan. During a visit to Ruusan by bounty hunters Beilert Valance and T'onga, who were searching for Valance's past mentor, Nakano Lash, the nexu, along with several local inhabitants, launched an attack on them in an effort to protect Lash. Valance engaged the nexu in combat, but the nexu's trainer intervened, and after discovering Valance's identity, guided them to Lash's whereabouts. Following the nexu's owner's rescue of T'onga, who was shot and almost killed, he dispatched a message to Losha Tarkon, the hunter's spouse.
Once Tarkon made her way to Ruusan, T'onga came back to consciousness. T'onga planned to embark on a mission to bring the criminal conflict between the Unbroken Clan and the Mourner's Wail Syndicate to a stop, and wanted Tarkon to join her. The owner of the nexu gifted it to T'onga and Tarkon so that it could aid them in their mission. Tarkon later started referring to the nexu as Furball.