Zeus, Poseidon, and Hades were all born from Titans. Eventually the three brothers defeated and killed the Titans.
Poseidon and Astypalia
Once the three brothers defeated the titans they drew lots to divide up the powers of the world. Zeus got the heavens, Poseidon got the oceans, and Hades got the Underworld. Poseidon become second in power.
Agaeus and the Island.
Cecrops was the first king of Athens and he wanted someone to rule. Both Athena and Posedion wanted to rule Athens. Cecrops asked for a gift for Athens and the best gift given would win Athens. Athena won the competition and in return Poseidon put a drought in Athens.
Poseidon falls in love with a sister of Europe named Astypalia. He abducted her and they gave birth to a son named Agaeus.
Agaeus lived on a island and he owned and operated a vineyard there. He treated his workers poorly.