In Frank Herbert's Dune...?

As I recall, Herbert set up the whole interplanetary government system after Medieval European feudalism. There was a strong nobility present (of which Paul's family, the Atreides were part) and a galactic emperor in place of a king. These noble families would rule over the individual planets at the pleasure of the emperor. (Their moving around somewhat parallels how English monarchs would give their noble friends governorships of prosperous colonies). You also had the Guild, who had a monopoly on trade and transit, somewhat ogous to entities like the East India Trading Company, and the Bene Gesserit, who are the equivalent of the Catholic Church, possessing influence and power all over the galaxy, oftentimes able to challenge the emperor. Look back at a bit of your European history, and it should start to make a bit more sense.