Theseus

"The Labyrinth is treacherous. There is only one thing that saw me through: the love of a mortal girl. The string was only part of the answer. It was the princess who guided me."

- Theseus to Nico di Angelo

Theseus is a Greek demigod, a son of Poseidon and the mortal Aethra. He became the King of Athens.

History
When Aegeus found out Aethra was pregnant, he returned to Athens. He met up with Medea, who had fled Corinth after she had killed Jason's wife. Some stories say she killed Aethra's children with Jason, but denied it and said the townspeople killed them in The Lost Hero.

Theseus on his way to Athens encountered and defeated the giant Procrustes who lure travelers on to a bed and stretched or shortened his victims to the perfect size for his two beds. Theseus defeated him by trapping him in his own bed, although it is not said whether he straightened or shortened him. He also defeated: Periphetes (the clubber); Sinis (the bender of pines); Crommyonian Sow (a big pig type monster); Sciron (pushed his victims from cliffs); Cercyon (the wrestler). He killed all of them doing the same thing they did to their victims.

When he arrived at Athens, he did not introduce himself immediately, and his father was suspicious of the stranger. However, Medea recognized him and worried that he would be given the crown instead of her son Medus. She challenged him to capture the Cretan Bull. He returned to Athens victorious, but Medea planned to poison him. At the last second the king recognized the sandals, shield and sword that Theseus was wearing as the ones he had left under a boulder for his son. He knocked the poisoned wine out of Theseus' hands, and Medea fled.

Theseus, after King Minos kidnapped some Athenian boys and girls to sacrifice to the Minotaur, decided to descend into the Labyrinth to save them and once and for all kill the Minotaur.

On the third occasion, Theseus volunteered to slay the monster. He took the place of one of the youths and set off with a black sail, promising to his father, Aegeus, that if successful he would return with a white sail. Like the others, Theseus was stripped of his weapons when they sailed. On his arrival in Crete, Ariadne, King Minos' daughter, fell in love with Theseus and, on the advice of Daedalus, gave him a ball of thread. This was so he could find his way out of the Labyrinth. That night, Ariadne escorted Theseus to the Labyrinth, and Theseus promised that if he returned from the Labyrinth he would take Ariadne with him. As soon as Theseus entered the Labyrinth, he tied one end of the ball of string to the door post and brandished his sword which he had kept hidden from the guards inside his tunic. Theseus followed Daedalus' instructions given to Ariadne; go forwards, always down and never left or right. Theseus came to the heart of the Labyrinth and also upon the sleeping Minotaur. The beast awoke and a tremendous fight then occurred. Theseus overpowered the Minotaur with his strength and stabbed the beast in the throat with his sword (according to one scholium, Theseus strangled it on Pindar's Fifth Nemean Ode).

After decapitating the beast, Theseus used the string to escape the Labyrinth and managed to escape with all of the young Athenians and Ariadne as well as her younger sister Phaedra. On the return journey Theseus abandoned Ariadne on the island of Naxos. In other versions of the story, the god Dionysus appeared to Theseus and told him that he had already chosen Ariadne for his bride, and to abandon her on Naxos an island where they stop to get some rest. Ariadne then cursed Theseus to forget to change the black sail to white. Seeing a black sail, Theseus' father Aegeus committed suicide by throwing himself into the sea (hence named Aegean). Theseus and the other Athenian youths returned safely. Theseus returned safely back as a king of heroes.

Theseus and Pirithous went to the underworld in order to capture Persephone. Hades enraged called the Furies to punish Pirithous and enjailed Theseus into his palace doors. While the first hero was freed by Hercules a few months later, Pirithous stayed there. Even after freedom, he perished miserably in exile.

The Titan's Curse
Dionysus stops Percy Jackson and Blackjack while they were following Thalia Grace, Grover Underwood, Zoë Nightshade and Bianca di Angelo. Dionysus tells Percy that you can never trust heroes because of the account that Theseus 'dumped' Ariadne on the island Naxos, betraying her. Because she was beautiful, Dionysus healed her broken heart and married her.

The Battle of the Labyrinth
He appeared while Nico di Angelo was trying to summon Bianca. Percy thought that Theseus was a 'middle-aged, buff guy' until he saw his ghost, which surprised him. He looked about the same age as Percy which at that time was 14. The ghost states that Aegeas was his stepfather.

The Last Olympian
He is briefly mentioned by Paul and Nico while they are discussing how Percy will send a signal to his mom and Paul Blofis if he defeats Kronos.

Paul suggests, "Like Theseus. He was supposed to raise white sails when he came home to Athens," to which Nico replies, "Except he forgot, and his father jumped off the palace roof in despair. But other than that, it was a great idea."

Abilities
As a son of Poseidon; one of the Big Three, Theseus was an extremely powerful demigod. He has divine authority over his father's domains and subjects. However, all is the following is conjecture, since Theseus has only ever been seen as a ghost in the Series.

Water-Induced Abilities: When in contact with or in the presence of water, Theseus gains a disproportionate amount of superhuman clarity, strength, speed, agility, and endurance equaling a god. However, this only lasts for a limited amount of time unless he is completely submerged in water. He also heals himself from any wound and most poisons when he comes into contact with water, the amount of water and time needed for the healing being proportionate to the severity of the wound.

Hydrokinesis: With the power of the sea within him, Theseus can control every form and great volumes of water, being even able to summon and heal his wounds and cure himself of most poisons with it. Theseus can control water almost omnipotently. He can control it in order to make it explode, or use it to grab something. His hydrokinesis abilities include: Aerokinesis: Theseus can summon hurricanes and other types of storms, but the extent to which he can control them is as of yet unknown.
 * General Hydrokinesis: He can create water from petrified seashells, as well as being able to create water with his own energy and summoning the "force of the ocean" to his will, as long as he concentrates hard enough. He can also harden water into an almost solid shape.
 * Hydrogenesis: Theseus can create water from his own power, though it takes much of his energy for him to do so. He also uses this skill while creating his own personal hurricanes.
 * Healing Factor: Since he is the son of Poseidon he can heal most wounds and cure most poisons when in contact with water.
 * Water Propulsion: He can control the water around him to propel himself through water. Theseus can shoot water, not only from being in water, but he can blast the own water he creates.
 * Underwater breathing: Theseus can breathe underwater and diffuse the oxygen in the water to create oxygen bubbles that allow his non-hydrokinetic friends to breathe underwater.
 * Water Immunity: Theseus can fall from great heights into water, and is unaffected by any amount of water pressure. He does not get wet if submerged in water, unless he wants to. Theseus can dry items underwater (as long as he holds onto it.
 * Water Solidification: Theseus can harden water into an almost solid shape. He can use this power to walk on water, by increasing the surface tension of the water to the point where it is solid enough for him to stand on, and water constructs.
 * Sailing Skills: Theseus possesses an intimate awareness of any ship he is on (sailing ships, canoes, motorboats, possibly submarines); being able to telekinetically operate one (as well as anything related to the ocean) because he has perfect bearings on the ocean, he can easily navigate his way at sea.
 * Communication: Theseus has divine authority over and can talk (normally and telepathically) to equines and sea creatures who mainly treat him with deference and lordly respect. He can also speak to other children of Poseidon underwater.

Geokinesis: Theseus can generate earthquakes and (consequently) cause volcanic eruptions, but his control of this technique is less than that of a child of Hades.

Cryokinesis: Theseus can use cryokinesis to a small degree. He is able to use the ice and snow around him to make an icy hurricane.

Electrokinesis (limited): Theseus can make sparks of lightning appeared as his hurricane increased in power. His control of this ability, however, is far less than that of a child of Zeus and appears to be a limited side effect of his storms.

Trivia

 * Percy, another son of Poseidon, also slayed The Minotaur.
 * Theseus, like Percy, inherited their father's green eyes.
 * Theseus was mentioned in The House of Hades.
 * In The Lightning Thief, Percy, another son of Poseidon, also fought Procrustes and killed him the same way.