Thornclaw is a golden-brown tabby tom of ThunderClan. He is the younger brother of Brackenfur and "twin" of Brightheart. His sister-in-law is Sorreltail, and his nieces are Cinderheart and Poppyfrost. His nephew-in-law is Berrynose, and he now has great-nephews or nieces, with the arrival of Berrynose and Poppyfrost's kits in The Fourth Apprentice. He is also the brother-in-law of Cloudtail, uncle to Whitewing and uncle-in-law to Birchfall, and great-uncle to Ivypaw and Dovepaw. He has amber eyes and is known to be ambitious.