This is the character she sets against a backround of Mycenean Greece and Minoan Crete, where the sky-god worshipping Hellenes are recent invaders whose culture is at odds with that of the indigenous earth-mother worshipping Shore People.
In The King Must Die Ms. Renault takes us through Theseus' childhood in Troezen as he learns that he may not be the son of Poseidon after all, although he certainly seems to be favoured by the god, and eventually that he is the son of King Aigeus of Athens. He sets off to seek his father, crosses the Isthmus and comes to Eleusis, a Shore People state where the reigning Queen takes a husband each year, only for him to be sacrificed in a wrestling match to the death to ensure the fertility of the crops. Theseus is chosen to fight the previous year's king and become king in his stead. Theseus does not succumb when his year as king is up and continues on his way to Athens. Once recognised as Aigeus' son he unites the two states and incidentally founds the Eleusinian mysteries with the help of Orpheus.
Theseus voluntarily goes off to Crete with the Athenians chosen as tribute to serve as bull dancers in the Labyrinth, the great palace at Knossos. It was the famous picture of the bull dancer there that inspired Ms. Renault to write the book and it shows. This is the emotional heart of the book -- I don't think anyone could read it and not want to be a bull dancer.
King Minos of Crete is slowly dying. Theseus plays a crucial role in the resistance against Minos' stepson Asterion, also known as the Bull of Minos (Minotauros) succeeding. In the chaos after the earthquake and tsunami caused by the eruption of Thera, Theseus and the bull dancers escape from Crete accompanied by Minos' daughter, the Goddess on Earth, Ariadne. In Naxos, Ariadne takes part in the rites disposing of the king after his one year reign, which are even more extreme than those in Eleusis, and Theseus leaves in horror while Ariadne is asleep. He doesn't change the sail as he promised his father, and Aigeus leaps to his death. This is where the first book ends.
Back in Athens at the beginning of The Bull From The Sea, Theseus' main problems after the burial of his father are the re-integration of the bull dancers back into Athenian life and the increase in piracy after the overthrow of the Cretan thalassocracy. While dealing with the latter problem he becomes friends with Pirithoos, the freebooting son of the King of the Lapiths, and joins him on his voyages rather than deal with the problem of what to do with Phaedra, another daughter of the late King Minos.
On the voyage, Theseus meets Hippolyta, the Queen of a group of Amazons. He falls in love with her, defeats her in single combat, and by the terms of the fight takes her back to Athens with him. They cannot marry because the Athenians would not accept her as queen, but they have a son, Hippolytus. Hippolyta encourages Theseus to marry Phaedra, but keep her in Crete to rule there. After Hippolyta is killed during a great invasion by the peoples of the North, Theseus brings Phaedra and his son by her to Athens. Hippolytus is brought up by Theseus' mother in Troezen. Phaedra later accuses Hippolytus of rape after he rejects her advances and Theseus curses Hippolytus, who is killed in another tsunami. Theseus goes back to freebooting and has a stroke. Seeing what a mess his cousin makes of Athens while he is incapacitated, Theseus decides to retire to Crete but stops off on the way in Skyros, where he commits suicide by leaping off a cliff.
As can be seen from the above summary, Ms. Renault's story follows Plutarch's biography of Theseus, supplemented by early 20th century archaeological discoveries and anthropological speculations. Few scholars nowadays would accept the idea of a cultural, political, and military struggle between invading Indo European Hellenes who worship a sky god and indigenous pre-Indo Europeans who worship the earth mother in a matriarchal society where the Queen's consort is killed each year as the dying and rising god of vegetation, let alone the idea of the Kentaurs (Centaurs) as Neanderthals. Nevertheless, The King Must Die and to a lesser extent The Bull From the Sea remain utterly compelling as recreations of a legendary age. These are people who might have lived rather than 20th century people dressed in Mycenaean clothes. One particularly nice touch is the very natural way characters, particularly Theseus himself, ask the type of questions characters in Greek plays ask in stichomythia and which sound so odd on stage. Yet here they sound perfectly reasonable.
It does have to be said, though, that The Bull From The Sea is less of a masterpiece than The King Must Die. Having started the story of Theseus, Ms Renault felt she was duty bound to finish it off, and in places it shows. Neither Theseus' relationship with Hippolyta nor his relationship with Hippolytus can quite take the place of the bull court as the emotional heart of the book and it does become one damn thing after another, superbly told but lacking in unity. In fact the most intensively emotional part of the The Bull From The Sea is Theseus' meeting with Oedipus, taken from Sophocles' Oedipus at Colonus. As just one incident with no real anticipation or aftermath, though, it is not enough to carry the whole book. For this reason, quite apart from questions of chronological order, I would definitely recommend reading The King Must Die first, but don't let that stop you from reading The Bull From The Sea if you really can't get hold of the first book.