Thalia Grace is the daughter of Zeus and Beryl Grace, a TV starlet the god met in the 1980s. She was born on December 22, 1987, 7 years earlier than her brother Jason. In The Lost Hero she is revealed to be the older sister of Jason Grace.  Due to her mother's abusive nature, Thalia has considered leaving home since she was little, but stays to protect Jason from her mother's antics. However, when Jason is apparently killed during a visit to Sonoma (in actuality, he is merely presented to Hera), Thalia finally runs away at age 10 and stays with Luke and Annabeth until they meet Grover Underwood when she is 12. When the party reaches Camp Half-Blood, Thalia gives her life to hold off pursuing monsters on top of what would later be called Half-Blood Hill. To save Thalia's life, her father transforms her into a pine tree. Her spirit then provides a magical barrier that protects the camp until seven years later when it is purged from the pine tree by the Golden Fleece .