[Destriarch]

Space nomads isn't a bad analogy, from what I've read. They act rather like tribes, they have their own rules and rituals, it seems that honour is important to them and they call duels between each other to settle rivalries, and there are several different clans mentioned each with their own agendas. In fact the trader clans are about the only part of the background chapter that seems to be fairly well fleshed-out, so presumably they are important to the series as well. There's a slight atmosphere of 'Dune' about them, although not as cool as Frank Herbert's masterpiece.

Ash