Sardaukar are the soldiers of House Corrino, at the time of Dune the house of the Emperor. Until Leto Atreides discovers the Fremen on Arrakis, they are the foremost soldiers in the universe, and are feared by all. They are the backbone of the Emperor's strength.
Sardaukar are trained from infancy on Salusa Secondus. What the rest of the universe knows as the Emperor's prison planet, few realize is the training ground for the hardiest soldiers. Like the Fremen on the planet Dune, the intense difficulties of simply surviving on Salusa Secondus leave only the toughest alive, and in conjunction with intense conditioning for loyalty to the Emperor, the Sardaukar are worth ten times their number in house levies.