- More details, see Guild Navigator
A Steersman was another name for Guild Navigators of the Spacing Guild. They are deformed because of the deep exposure to Spice Melange and the zero-gravity life in space. The high exposure to spice is necessary to develop the linear prescience to guide the spaceship through the safest path during the folding space.
The concept was further fleshed out in that advanced Navigators were steersmen, and that Navigators with far less experience were called pilots.