Gadieros was the son of Poseidon and the Mortal woman Cleito, who bore five sets of twins. These ten demigods were given rulership of Atlantis, with the eldest, Gaderios twin, Atlas was given rulership over the other nine and over Atlantis the city. The realm of Gadieros was the extremity of Atlantis closest to the Pillars of Hercules and one of the last to sink beneath the waves. Poseidon saved his Gadieros, and perhaps others of his sons, by bringing them to his Realm after the destruction of Atlantis. There he faithfully served his Father for millennia while the world turned and everything Gadieros knew turned to dust and was forgotten.
A being of obvious supernatural origin is sent to Magnus and Duncan claiming to be Gadieros and that Poseidon has ruled that it is time for Atlantis to return to the world of men. Gadieros is sent as a sign of Poseidon's favor for their endeavor and is instructed to assist them. Gadieros is a potent leader of men, and as annointed king of a portion of the island, may find his influence useful, depending on what survived and to what degree they owe allegiance to the old ways.
Gadieros is extremely reluctant to speak of details of Old Atlantis, save trivial details of everyday life. Specifically he is most reluctant to speak of the war, the sinking of Atlantis, or the aftermath.