Luke Castellan is one of the main antagonists (being a traitor) in Rick Riordan's Percy Jackson & The Olympians series. He is a demigod son of the Greek god Hermes.

Luke is played by Jake Abel in the movies Percy Jackson & the Olympians: The Lightning Thief, the film adaption of the first book, The Lightning Thief and Percy Jackson: Sea of Monsters, the film adaption of the second book The Sea of Monsters.

Character background
Luke is first introduced in The Lightning Thief as the 19-year-old counselor for the Hermes cabin. He was born the year 1986. While the rest of Percy's cabin mates complain about him because he is undetermined, Luke tries to make him feel at home, even stealing a toiletry bag for him. Luke first came to Camp Half-Blood when he was 14, alongside Thalia Grace, daughter of Zeus, and Annabeth Chase, daughter of Athena. Luke has a scar on his face, a relic from his battle with the dragon Ladon, guardian of the Garden of Hesperides, while on a quest. In The Last Olympian, it is shown that his mother attempted to become the Oracle of Delphi and has succumbed to the curse of Hades. Her crazed prophetic ramblings affected Luke greatly, and forced him to run away when he was nine. In The Battle of the Labyrinth, Luke's body becomes the vessel that harbors Kronos' essence.

Luke dies in The Last Olympian when he is given Annabeth's knife by Percy. He sacrifices himself to defeat Kronos by stabbing himself under his left arm where his mortality was still kept intact after his bath in the River Styx (known as his Achilles heel). As he dies, he asks Percy to make sure all the demigods are claimed to avoid this happening again which might mean that they had become friends again because he is forgiven by Percy. Although he is seen as a villain throughout the series, in the end he is treated like a hero and forgiven by everyone. He is also the hero mentioned by the prophecy of the Oracle in The Last Olympian.

Power/abilities
 Luke has ADHD like other half-bloods, which allows him a heightened awareness in combat.
 As with most other half-bloods, Luke is dyslexic because his brain has been "hard-wired" to read Ancient Greek.
 Luke is said to be an amazing fighter and swordsman, "The best swordsman in 300 years", as mentioned by a Hermes camper in The Lightning Thief, although Thalia Grace, his old friend, can always beat him in battle.
 He has the Curse of Achilles, which gives him near invincibility except in one part of his body (in this case, beneath his left arm).
 His soul is fused with Kronos', giving him Kronos' abilities.
 Being a child of Hermes, Luke has abilities that involve traveling and theft. He has displayed such powers twice. In The Lightning Thief, he slashes through the air and disappears through the ripple he created. In The Titan's Curse, he conjures up a pool of water and a sacrificial fire by waving his hand.
 Strong willpower, as evidenced by his ability to host Kronos in his body without completely losing his identity.
He also can use powers to break locks and open doors

Weapons/magical items
Backbiter – a blade with one side of celestial bronze melded with tempered steel. The celestial bronze allows for the wounding of immortals and monsters, while the steel injures mortal. Backbiter is a foot longer than Anaklusmos, Percy's sword. Percy sensed a tragedy in the making of Backbiter. In the fourth book, it is revealed that the metal used for Backbiter came from Kronos's scythe. It is reforged into its original form for its master's rising.
 A pair of magical sneakers that can sprout wings when the owner says, "Maia", the name of Luke's paternal grandmother. The sneakers were given to him by his father Hermes and bear a close resemblance to Hermes's own winged shoes. In The Lightning Thief, Luke cursed them into pulling the wearer of shoes into the pits of Tartarus; however, since Grover put them on instead of Percy it confused the curse. The shoes are now gone, for they slipped off of Grover and fell into Tartarus.
 Kronos's Scythe – when Kronos is brought back to life in Luke's form, the telekhines gave him Kronos's scythe, which is reforged out of Backbiter. No amount of celestial bronze can beat it.

References

Other websites
Official UK site 

Percy Jackson and the Olympians characters