For the planet, please see Neptune.
Neptune was the Roman god of water and the sea in Roman mythology and religion.
In 2266, Anton Karidian performed the line from Macbeth, Act II, Scene II: "Will all great Neptune's ocean wash this blood clean from my hands" on Planet Q. (TOS: "The Conscience of the King")
Neptune was worshiped on planet 892-IV too, but the Children of the Son considered him a false god. Neptune Bath Salts were named after him. (TOS: "Bread and Circuses")