Thalia Grace

Thalia is a demigod, a daughter of Zeus. She was a friend of Annabeth Chase and Luke Castellan. She is famed for being turned into a tree to save her friends. Percy revived her from her tree form in The Sea of Monsters and was thought to be the Chosen One by The General. However, she became an immortal hunter, ensuring that she never turned sixteen to fulfill The Prophecy. She was offered a spot as an immortal hunter by Artemis, and she accepted so not to be the child of the prophecy. Thalia being the daughter of Zeus can control lightning. She is afraid of heights, which is odd since her father is Zeus. This is shown in The Titan's Curse, after Thalia flies Apollo's sun chariot. Thalia, at that time, appears to be horrified and doesn't fly well.

Early Life
Thalia is a daughter of the mightiest of the Gods, Zeus. Her mother was a drinker, whom she didn't get on good terms with. Therefore, she ran away. She later met Luke Castellan, Annabeth Chase, and Grover Underwood. This was possibly when she discovered he demigod heritage. This was also when she began to forge a romantic relationship with Luke.

Sometime during their journey to Camp Half-BLood, they encountered the Huntresses of Artemis. Their lieutenant, Zoe Nightshade, offered her (and likely Annabeth) a spot in the group. Thalia refused to leave Luke behind (as a huntress would have to give up romance) and therefore refused the offer, forging a rivalry between the two.

Sacrifice
As the quartet travelled to Camp Half-Blood, they were pursued by monsters. A cyclops found them and held Thalia and Luke up in the air, directing the other monsters towards them. Annabeth saved the two by stabbing the cyclops in the foot. The monsters began to catch up, so Thalia made the ultimate sacrifice: she elected to stay behind so they could make it safely to Half-Blood Hill. It is unknown whether she actually fought the monsters or not, but she most likely fought them and was mortally wounded. The Gods, impressed by her bravery, saved her life by turning her into a tree, later renamed Thalia's Tree. This tree became a barrier against monsters.

Abilities
Thalia is described by Percy Jackson as being a terrifying opponent on the battlefield. She wields a spear and a shield called Aegis, which bears the head of Medusa on it. As the child of Zeus, she's able to control lightning. Her abilities in combat are satisfactory enough to earn the respect of the General and defeat Luke, a prodigious swordsman (and former love interest) in combat.