Born in Atlantis, Kastor is the son of Arkantos and has never known his mother, who was killed by pirates many years ago. Kastor sees himself as a great warrior, but, although brave, he is not quite what he thinks he is. He would love nothing more than to fight a war by his father's side. Kastor sometimes spends time looking after the Theocrat Krios's horses. In Fall of the Trident, he is fourteen years old and, although he wishes to accompany Arkantos to the Trojan War, is told to stay home in Atlantis.
In Fall of the Trident, Kastor is a weak hero unit who wields a sword. In The New Atlantis, Kastor is 24 and the main protagonist. In the end, he becomes the leader of the Atlantean empire. He is a hero unit whose special ability is a powerful sword attack which sends human units flying.