Longwang (the Dragon Kings) vs Poseidon

The dragon kings who rule the waters and send the rain, most famously the Dragon Kings of the Four Seas led by Ao Guang of the Eastern Sea. They govern as officials of the heavenly bureaucracy under the Jade Emperor, and their temples stood in villages across China wherever farmers prayed for rain.

The Dragon Kings grew from the ancient Chinese association of dragons with water and rain, combined after the arrival of Buddhism with the naga kings of Indian scripture. Popular religion made them officials appointed by the Jade Emperor over each body of water.

The belief that dragons control water and rain is ancient in China. With the arrival of Buddhism, the Indian naga kings of the sutras, serpent rulers of underwater palaces, merged with native dragon lore to produce the Dragon King (Longwang). By late imperial times every sea, river, lake, and well could have its dragon king, and the most prominent were the four kings of the Eastern, Southern, Western, and Northern Seas.

God of the sea, earthquakes, and horses. Brother of Zeus and Hades, ruler of the oceans and all waters.

Poseidon rules the vast oceans, earthquakes ("Earth-Shaker"), and horses. He is a moody and tempestuous god, much like the sea itself. Sailors prayed to him for safe passage, often sacrificing horses or bulls to appease his wrath.