Julian Solo was a rich heir of an important marine merchant of Greece.
Curses of Poseidon
Poseidon always possesses a member of Solo family, because they are important rules of the sea. According to Julian, the sea is the majority of world surface, ergo, when domains it, domains the world
Julian was possessed by Poseidon in his 3 years old, but Poseidonseeps into his body.
In the sea (he always lived near the sea), he founds a fish, and frees it, and thinks it is a cute and beautiful fish.
On his birthday of 16 years old (his father died recently), he has already chosen the rich Saori Kido as his wife to rule in the sea with him, but she refuses, to surprise of Julian, that never was refused.
Thetis, appears in that party, over the Poseidon's Temple Ruins, and Julian arrives there after seeing the glow of the Trident of Poseidon. Thetis takes Julian to the Poseidon's Temple, and here, she says to him, that he is Poseidon; she already thinks Julian is possessed by Poseidon, and call him "Kaiō Poseidon", because Kanon doesn't tell to her Poseidon is sleeping and need be awake (but hits will awakes Poseidon unwittingly). So, Julian thinks is Poseidon and gets his memories, but still is Julian (his confuse; but Julian after Poseidon begin awake, gets confused too and doesn't know who is he). When Saori arrives at the Poseidon's Temple, he asks her to marry him and the two gods will rule in the new world after the flood, but she refuses.
After the battle with Seiya, Poseidon takes full domain in the Julian body (before, the body was dominated by Julian altered because he has been under Poseidon badness). After the soul of Poseidon have sent to the amphora, Julian was lost by Saori, and Thetis, always together Julian, helps him and dies, turn back a fish.... she was the fish that Julian saved, and so, she must serve Julian too, and don't only Poseidon.
After the procession, Julian doesn't remember anything, so, he will use his fortune to help victims of the flood (that generated sequelae in the world, different of the Hades eclipse) that he caused (he does not remember that), and Sorento meets him (he already met him, but as possessed by Poseidon's evil) and offers help him playing his flute for kids. Julian finds Thetis as a fish, remember something about this fish (Sorento know who is it) and free his body in the sea again.
Julian was possessed by Poseidon again in Omega.