Kathy works as a "carer," a clone who cares for other clones once they begin donating their organs. In the backstory, she's raised and educated at a special boarding school called Hailsham, where she becomes friends with Ruth and Tommy. Kathy later becomes Tommy's carer and watches him "complete," or give his final donation.
Tommy grows up with Kathy and Ruth at Hailsham. In school, he's an excellent student, but a poor artist, and is often teased because of his lack of artistic talent. He has a long-term but complicated relationship with Ruth while at Hailsham and the Cottages. Later, he dates Kathy, who becomes his carer.
Ruth attends Hailsham with Kathy and Tommy. Ruth is perhaps the most social of the three, and she distances herself from Kathy and Tommy as the novel progresses. Later, she admits to dating Tommy just to keep him and Kathy apart. Of the three friends, Ruth dies first.
Miss Geraldine, one of the guardians at Hailsham. She's the preferred confidante of the younger children and is generally considered the most sympathetic of the guardians.
Miss Lucy, another guardian at Hailsham. She's not as nice as Miss Geraldine, but, as Kathy and Tommy later learn, works harder to convince outsiders that clones have souls and should be treated with respect.
Chrissie and Rodney
Chrissie and Rodney, two "veterans" of the Cottages who convince Ruth that they've seen a "possible" (a woman from whom Ruth may have been cloned). They convince Ruth, Tommy, and Kathy to go to Norfolk to see the possible. This is a ruse to get the Hailsham graduates to talk about "deferment," or the process of deferring one's donations.
Madame, the official who regularly visits Hailsham to select student artwork for the Gallery, where the guardians at Hailsham exhibit the students' art to prove that clones have souls. Madame later admits to being repulsed by clones, in spite of her efforts to improve their living conditions.