In the Dune universe created by Frank Herbert Guild Navigators are humans mutated through high consumption of the spice melange, who is safely able to navigate interstellar space in a Heighliner. Guild Navigators are specially selected for their prescience, which is required for their position. Continuous immersion in highly concentrated amounts of orange spice gas and a micro-gravity environment changes their body as the spice develops their prescient abilities.

The first external sign of spice-mélange induced metabolic change is that eyes become blue on blue. For those who wish to hide their use of large doses of spice, efforts must be taken to hide the entire eyeball that has become tinted blue. This is done through the use of large contact lenses that cover all the space visible between the eyelids. Few people have actually seen a Guild Navigator: They use envoys and ambassadors to present a human face and hide their deformity from those with whom they deal.

Guild Navigators are in fact greatly mutated humans who appear almost amphibious, with enlarged heads, a triangular mouth, and atrophied extremeties on bloated bodies. Although their appearance was a mystery in the original novel Dune, one is fully revealed in the first chapter of Dune: Messiah. Here, the Guild Navigator Edric (Dune) is described as having rodent-like eyes, a thin fish-like mouth, webbed feet, and grossly elongated fingers and hands.