One of the great houses of the Imperium. The House Harkonnen is built on a simple foundation of fear and terror, two tactics that make the Baron Harkonnen's underlings that much more dangerous: risk death on the battlefield or suffer a slow, excruciating death in the Baron's chambers as he watches with relish. With an order based on treachery, soldiers rise through the ranks through deceit, trickery and, if necessary, assassination.
Hailing from an industrial wasteland of a planet called Giedi Prime, the House Harkonnen is much like its Baron: cold, ruthless, egomaniacal, but brilliant and lethally efficient. Most of all, it's driven by a kanly (vendetta) against House Atreides, which the Harkonnen feel has taken what's rightly theirs: the whole planet of Arrakis and the spice Melange.
House Harkonnen is ruled by a Siridar Baron. In the first Dune novels the baron is Vladimir Harkonnen. The twisted mentat Piter De Vries served as the barons mentat and advisor.