Rookthorn was born as a RiverClan kit and had a relatively normal upbringing. She was born an only kit so her mother Oakblaze was always quite protective over her, although she insisted that it was unnecessary. When she was an apprentice, Rookthorn had a mentor named Beechfur, who was an aggressive and rigid cat. While he was never mean to Rookthorn, his ideals sort of rubbed off on her. This led to a shift in personality. Rookthorn went from a curious and accepting cat to a closeminded but formidable warrior who would not hesitate to strike any outsiders. While she may be unfriendly towards anyone not in RiverClan, she is fiercely loyal and caring to her own clanmates. Rookthorn would do anything to defend them.

She is mates with another RiverClan warrior named Softflower, whom she met when Softflower joined RiverClan after being a loner. Knowing Softflower has helped Rookthorn open up to the possibility that not every cat that isn't from her Clan has bad intentions.