Without the Navigators the Imperium would fly apart, its worlds severed from one another across an ocean of hostile warp. These are the scions of the Navis Nobilite, an order of noble houses so ancient that it predates the Imperium itself, and every one of them is a mutant, for set into each Navigator's brow is a third eye, the Warp Eye, with which they alone can perceive the guiding light of the Astronomican and chart a course through the shrieking currents of the Immaterium.
The gift is inseparable from the curse. Untold generations of careful breeding to preserve the precious Navigator gene have left the great houses marked by strange afflictions: bodies grown tall and spindly, skin gone pale and translucent or hardened into scales, features ill-formed and eyes too large. The Warp Eye itself is deadly to behold, and a Navigator who unveils it can wither the sound mind of an ordinary mortal in an instant. So it is that these indispensable nobles are also shunned and feared, tolerated only because the Imperium cannot live without them.
Upon the battlefield a Navigator is a weapon as much as a guide. When threatened, they need only draw back the wrappings that hide their third eye and turn its gaze upon the enemy, unleashing a raw pulse of the warp that boils the very thoughts from a victim's skull. Bound to Rogue Trader dynasties, naval vessels, and Inquisitorial retinues alike, they lend their unnatural sight to those who can endure their presence, ever loyal to their distant houses and to the Paternova who rules them all.