Lionheart was a deputy of ThunderClan under Bluestar's leadership in the forest territories. He was born to Speckletail and Smallear as Lionkit, along with his sister, Goldenkit. He became an apprentice named Lionpaw and was given Swiftbreeze as his mentor. During his apprenticeship, he witnessed Pinestar visiting the Twolegplace, but told nothing to his Clanmates when Pinestar asked him. However, when Pinestar decided to leave ThunderClan and become a kittypet, Lionpaw convinced him to tell the Clanabout it himself, and Pinestar said that he would have named him Lionheart. Sunstar granted him this name, Lionheart, when he became a warrior. He was given Graypaw as his apprentice and trained him and Firepaw when the kittypet tom joined ThunderClan. Lionheart is a loyal and noble ThunderClan tom, skilled and strong in battle.