Brightheart, is a white she-cat with ginger patches along her back and a ginger tail, is a ThunderClan warrior introduced in Forest of Secrets. Brightheart was an apprentice, Brightpaw, for an unusually long period, along with her fellow apprentices Cloudpaw, Thornpaw, and Swiftpaw due to Bluestar's paranoia and refusal to trust her warriors following Tigerclaw's exile. Brightpaw develops a strong friendship with Cloudpaw, and is the first apprentice to congratulate him after his promotion to warrior status (received just for being Fireheart's apprentice) despite the other apprentices feeling jealous and angry. She eventually joins an expedition led by Swiftpaw into the lair of the dog pack during A Dangerous Path in an attempt to prove herself a warrior, which results in her being seriously injured as well as Swiftpaw's death.

Half of Brightheart's face is disfigured due to her injuries, including a missing eye and a scarred ear from a dog attack in A Dangerous Path. These features cause Bluestar to give her the warrior name of Lostface, which Firestar soon changes when he becomes leader. Though initially discouraged by her injuries, Brightheart is soon able to develop, with the help of Cloudtail, a system of fighting that makes use of her one-sided vision, making her as effective at fighting as any other warrior. She recoils from the sight of her own face and sometimes flinches when other cats are frightened by her scarred face. When not in battle, Brightheart is a kind and warmhearted friend to many warriors in the Clan. She adopts the duties of an unofficial medicine cat during the latter half of The New Prophecy series, becoming an object of Leafpool's jealousy, but quickly returns to being a warrior after Leafpool becomes ThunderClan's main medicine cat. In Twilight, Brightheart holds a grudge for Daisy, who often flirts and spends time with her mate, Cloudtail. However, after Leafpool points out to Cloudtail that he is hurting Brightheart (as he never loved Daisy, but is acting like he does), Daisy tells Brightheart that Cloudtail loves Brightheart, and by the Power of Three series, Cloudtail and Brightheart's relationship is as strong as ever.

Brightheart was apprenticed to Whitestorm, who also mentored her cousin Sandstorm, and had since taken Sandstorm's grandson Jayfeather as an apprentice, although this was only temporary due to Jaypaw later taking the role of medicine cat. She appears to have been hurt by this, likely due to her being desperate to prove to herself and the Clan that she can still function as well as a normal warrior. Despite Jaypaw's prickly attitude towards her during his apprenticeship, he is able to sense her feelings and is sympathetically warmer towards her upon becoming a medicine cat. Her mother is Frostfur, which makes her the littermate of Thornclaw, Cinderpelt, and Brackenfur. She and her mate, Cloudtail, currently have one daughter, Whitewing. She is also aunt to Poppyfrost, Honeyfern, Cinderheart, and Molepaw (Brackenfur's kits) grandaunt to Cherrykit and Molekit (Poppyfrost's kits), and grandmother to Dovepaw and Ivypaw (Whitewing's kits).

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