Legacy of the House of Haarlock.
Navigators are a very particular form of human mutant, possessing the navigator gene, which gives them the unique ability to navigate through Warp space. This ability makes them absolutely necessary to the Imperium’s continued survival.
All Navigators have a third eye, commonly called the Warp Eye, on their foreheads, which allows them to perceive the psychic light of the Astronomican, enabling them to fully use their powers in guiding ships through the currents of the Warp. Their ability to sense the tides of the Warp is considered psychic, although Navigators never possess any psychic abilities beyond the powers their Warp eye affords them.
Navigators possess natural life spans as long as four hundred years. As they increase in age, their abilities increase in power, and their physical appearance changes: the white and iris of the eye gradually disappears, leaving only a hardened black orb.
Because most humans fear and mistrust mutants and psykers, navigators are kept safely cloistered from society. Most humans are not even aware these creatures exist