The planet Neptune was named after the Roman God of the Sea.
Astronomers named Neptune after the Roman God of the deep sea to uphold the tradition of naming planets after mythical figures. The name wasn't only given because the colour of the planet resembles the ocean, the name also fits the planet well because of its position in "deep" space (deep sea - deep space).
The symbol for planet Neptune is the Trident (the weapon favoured by the God Neptune).
Neptune's largest moon was also named after the Greek God of the
sea's son, Triton.
Neptune was only referred to as "the planet exterior to Uranus" or as "Le Verrier's planet". The first suggestion for a name came from Johann Galle, who proposed the name Janus. Another proposal was Oceanus. Urbain Le Verrier, who discovered the planet, claimed the right to name his discovery: Neptune. Soon Neptune became the internationally accepted name.