In Chinese cosmology, heaven is ruled by the Jade Emperor (玉帝 yù dì), the underworld by Yama, King of Hell (閻王 yán wáng), and the oceans by the Dragon Kings.
In Journey to the West, Monkey visits Aoguang, Dragon King of the Eastern Ocean (東海龍王敖廣 dōng hǎi lóng wáng áo guǎng) who lives in a Crystal Palace (水晶宫 shuǐ jīng gōng) at the bottom of the sea. Monkey takes the Dragon King’s treasure, the Pillar that Holds Fast the Sea (定海神針 dìng hǎi shén zhēn, originally a stick for measuring the depth of sea water used by Yu the Great, controller of floods). The Pillar became Monkey’s famed weapon, the Golden-banded Staff (如意金箍棒 rú yì jīn gū bàng) that shrinks the size of a sewing needle and fits behind Monkey’s ear when he is not fighting.
I’m very fond of the Dragon King’s ineffectual army of shrimp soldiers and crab generals, which is used in modern Chinese as an idiom meaning ‘useless troops’.