Atreides-Harkonnen feud

The feud between House Atreides and House Harkonnen was an ancient blood vendetta that began at the Battle of Corrin and ran for ten thousand years, ending only with the annihilation of the Harkonnens on Arrakis. Frank Herbert gives only its root and its end; the story in between comes from the expanded books by Brian Herbert and Kevin J. Anderson. (Dune; Dune: The Battle of Corrin)

The Battle of Corrin#

Frank Herbert's Dune records only that the Baron is the direct male descendant of the Bashar Abulurd Harkonnen, who was banished for cowardice after the Battle of Corrin. (Dune)

In the expanded books, by 88 BG the League of Nobles had all but defeated the thinking machines of the Synchronized Empire under the evermind Omnius, who held only the planet Corrin. Vorian Atreides was Supreme Bashar of the Army of Humanity, and serving under him was Bashar Abulurd Harkonnen, grandson of Primero Xavier Harkonnen, who had once been Vorian's closest friend. When the League, driven by the fanaticism of the Cult of Serena Butler, launched the assault to destroy Omnius, a ring of orbiting cargo pods filled with human captives, the Bridge of Hrethgir, was revealed, rigged to detonate as the fleet passed. (Dune: The Battle of Corrin)

Abulurd disagreed with his commander and refused to cross the Bridge, unwilling to share in the deaths of two million. Vorian relieved him of duty and confined him, but Abulurd broke confinement and deactivated the weapons of the entire League fleet. The League still won, only more bloodily. For this Abulurd was branded a coward and, at Vorian's urging and with Viceroy Faykan Butler's agreement, banished. Vorian insisted he keep the shamed name of Harkonnen and swore his descendants would forever spit upon it. Exiled to Lankiveil, Abulurd raised a family whose children grew up on tales of the Jihad and came to hate the name of Atreides. (Dune: The Battle of Corrin; Sisterhood of Dune)

Griffin and Valya on Arrakis#

In 4 BG, in the expanded books, Vorian himself was exiled to the desert of Arrakis in exchange for the protection of his homeworld Kepler. He was tracked there by Griffin Harkonnen, Abulurd's ambitious great-grandson, who confronted him deep in a Zensunni sietch. A Fremen Naib told the two they had to fight to end their blood feud. In the struggle Griffin gained the upper hand but chose not to kill Vorian out of honour, declaring the feud over. The truce did not hold: hunters from Vorian's own past, the surviving children of Agamemnon, caught and killed Griffin in the desert before a sandworm swallowed them. Vorian sent condolences to Griffin's sister Valya Harkonnen, who spurned them and vowed revenge, leaving the feud far from ended despite her brother's intent. (Sisterhood of Dune)

The founding of House Atreides#

Feeling guilt over Griffin's death, Vorian secretly helped his struggling Harkonnen-blooded relatives, then travelled to Caladan to meet his Atreides descendants, among them Orry, Shander, and Willem Atreides. Tragedy followed: Valya and her younger sister Tula visited Harkonnen vengeance upon them in the name of the feud. Vorian duelled Valya on Wallach IX and was believed dead by his Caladanian kin, though he survived and began another new life. His relatives carried on without him, and Willem Atreides founded House Atreides itself in Vorian's honour and in opposition to the rising House Harkonnen. (Sisterhood of Dune; Mentats of Dune; Navigators of Dune)

The end on Arrakis#

The vendetta reached its conclusion in Frank Herbert's Dune, in the Desert War on Arrakis that followed the Harkonnen and Corrino plot against Duke Leto in 10191 AG and ended at the Battle of Arrakeen in 10193 AG. There the feud finally ended: Baron Vladimir Harkonnen was killed by Alia Atreides, and his nephew and intended heir Feyd-Rautha by her brother Paul, bringing about the end of the Harkonnens and the close of ten thousand years of bloodshed. (Dune)