His treecat name was "Shadowed Sunlight", later changed to "Shining Sunlight".
He was one of Alexandr and Evelina Zivonik's seven children. (HHA2.1: TS) He had a close relationship with Sumiko Uchida, who was taken in by the Zivoniks after the death of her entire family from the Manticoran Plague. Tragically, she was killed when saving one of his sisters from a falling crown oak branch. (SK1, SK2)
Karl eventually told Stephanie that he and Umiko had a big fight just before her death, and that he blamed himself ever since. Sharing this dark secret with others lifted a sort of veil from his mind-glow, leading to him being adopted by the treecat Survivor. (SK3)