Zeus also known as the Chief based on Homer, he is the most powerful off all because as you can say, he had been given the widest realm (the sky) to reign, while his brother Poseidon got the second largest (sea and oceans) and Hades the smallest (the underworld)
Zeus has control over the winds, lightning and many more while Poseidon has control over the waves, earthquakes and etc.
(this is based on my memory when my sister gave me her practice lecture about the Greek Gods and Goddesses.)
