Agamethus is the half-brother of Trophonius, the Dark Oracle.
Agamethus was the son of King Erginus and his wife. Trophonius was his maternal half-brother (his father was Apollo.) Agamethus and Trophonius grew up to become renowned architects. They even built Apollo's temple at Delphi.
Agamethus's death (and Trophonius's downfall) came after King Hyrieus commissioned the brothers to build his treasury. They became greedy for Hyrieus's wealth. They built the treasury with a secret tunnel. They planned to slip into the treasury in the dead of night, steal the valuables and slip out via the tunnel.
Unfortunately for them, Hyrieus had inspected every nook and corner of the treasury and discovered the secret tunnel. He had set up a rope-activated crossbow trap to trap any thief. His intention was to find out who planned to rob him.
When the brothers were coming out of the tunnel with the treasure, Trophonius sprung the trap without realising it. As a result, Agamethus got trapped in the tunnel, crushed under a beam. Trophonius was unable to pull his brother out. Trophonius prayed to his father, Apollo, to save Agamethus and take his life instead. However, Apollo refused to do so. Apollo told Trophonius that he and Agamethus had done something wrong, so they deserved a punishment.
Agamethus then decided to sacrifice his life. He told his brother to cut his head off, disfigure it and run away. This way, Trophonius would be saved and Hyrieus would be unable to discover the identity of the thieves. Trophonius, with a heavy heart, decapitated Agamethus and ran away.
Later, Trophonius turned into the Dark Oracle. Agamethus's spirit has accompanied Trophonius' spirit ever since.
Agamethus is first seen by Apollo, Leo, and Calypso in an alley as they run from blemmyae. After they are rescued and inside the Waystation, he reappears.
He communicates with others via his Magic 8 Ball, which pops up with what he wants to tell the reader when they shake it.
At the end of the book, after the Oracle of Trophonius had been blown up by Apollo, Apollo tells Agamethus that once he is a god again, he will try to get Agamethus a place in Elysium.
Agamethus, after his death, seems to have become wiser and more mature. He hasn't adopted an evil path. Rather, he has understood his misdeeds and repents for them. He has accepted his punishments with grace. He stays by his half-brother Trophonius, even though he has become the Dark Oracle. Agamethus has even forgiven Apollo for refusing to save his life at Hyrieus's treasury.
Agamethus seems to have become more friendly and helpful as well. He brought little Georgina to the Waystation so that she could be safe there. He also became friends with Emmie, Josephine and the other residents of the Waystation.
Agamethus's spirit appears as a typical Greek warrior, except that the head is cut off. He seems to be well-built with broad shoulders. He doesn't have a voice and he can't speak verbally.
Agamethus wears a traditional Greek chiton tunic and sandals. He keeps a sheathed sword by his side. His tunic is stained orange, due to blood trickling from his severed neck. He has a ginger-colored aura around him.
For some reason (choice or curse), Agamethus's spirit always appears like he was just before he died - his head cut off, his tunic covered with blood.
In life, Agamethus is described as having curly blond hair, a goofy grin, and broad shoulders.
- Trophonius: Agamethus was, and is, devoted to his half-brother. He sacrificed his life so that his brother wouldn't die. Agamethus's spirit has stayed with Trophonius ever since. Even after Apollo destroys the Dark Oracle, Agamethus leaves to find Trophonius and stay with him.
- Erginus: Agamethus probably loved and respected his father. He sacrificed his life so that Hyrieus wouldn't learn Agamethus's identity. Thus, Hyrieus wouldn't be able to attack the thieves' home, i.e., Erginus's kingdom.
- Agamethus is illiterate. Since he can't verbally speak or write down his message, communication with him was difficult.
- In the original myths, Agamethus was named Agamedes.