Poseidon was the Greek god of the sea who was given the island of Atlantis as his realm. The Romans later knew Poseidon as Neptune. Some writers have suggested that Noah was to be equated with Poseidon. His symbol was a trident. Poseidon is also credited to have been the first to tame horses. His first born of five sets of twin boys was Atlas. Some writers, such as Nienhuis, have equated Poseidon with Sidon referred to in Genesis 10:15.

The Phoenician sea god Melqart is frequently seen as the son of Poseidon whereas others, such as Jonas Bergman, consider them to be identical. The Nordic sea god Aegir is also seen as a mirror of Poseidon. In Portugal, Saint Bartholomew is considered a Christianised Poseidon where statues of him are similar to those of Poseidon including a trident.

The Celtic god of the sea was known as Manannán Mac Lir who is frequently associated with the Isle of Man in the Irish Sea.