Percy Jackson and the Olympians: Legends

He and Asterius wear identical clothes, with the only difference being that Theseus keeps his left shoulder uncovered and wears a wide belt around his waist. He is a muscular man who overdid the tan, his blond hair styled back (which in the past was long, similar to Achilles'), and he always maintains a confident expression on his face. His height is similar to Zagreus'. He can transform into a sophisticated battle outfit that includes a golden mask and ammunition on his chest.

Theseus, often proclaiming himself as "the great king of Athens," is a hot-headed, stubborn, and even childish ex-hero, but he is best known for his youthful exploits that were significant enough to earn him an immortal soul and boast for eternity in Elysium. Theseus has a very high opinion of himself and shows undying loyalty to Zeus and to the Sisters of Fate. Theseus has no respect for people deemed weaker than himself and belittles anyone who tries to change their fate. Theseus also appears to be a hypocrite.

Theseus's own birth was a complicate mess. His father was childless and asked the Oracle of Delphi for advice. He did not understand her prophecy and sought further advice from his host, king Pittheus of Troezen, who in turn understood the prophecy and thus got Aegeus drunk and gave him his daughter Aethra. However, following Athena's instructions, Aethra wandered off in the middle of the night to the island of Sphairia near Troezen. There, she poured a libation to Sphairos and Poseidon, and the God of the Seas possessed her for the remainder of the night. Thus Theseus was partly divine, as per usual in demigods. Theseus' soul appeared while Nico di Angelo was trying to summon Bianca's soul. Percy thought that Theseus had been 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 stated that Aegeus was his stepfather and that he recognized King Minos, who was there next to Nico.