Xavier Harkonnen was a prominent and highly respected military commander leading up to, and during, the Butlerian Jihad. He later murdered the Gand Patriarch Iblis Ginjo: an action that tainted his family's name for many centuries.
Early Life
Xavier was born to wealthy and prominent aristocrats within the League of Nobles, Ulf Harkonnen and Katarina Harkonnen. At the age of six, Xavier's parents were killed in an assault by thinking machines, and he was later adopted by Emil Tantor and Lucille Tantor.
Seen as an upcoming commander, Xavier received a military commission at the age of 19. Soon afterward, he distinguished himself in the Battle of Salusa Secundus by taking control of the shell-shocked League army and commanding them to a famous victory over the forces of Omnius, specifically a group of cymeks led by Agamemnon. During this battle his lungs were permanently damaged and subsequently replaced by Tleilaxu-supplied organs.
Relationship with the Butler Family
Following the battle, Xavier courted Serena Butler, daughter of Viceroy Manion Butler Senior. It was by Xavier that Serena conceived the martyr, Manion the Innocent, who she bore as a slave of the robot Erasmus on Earth.
After Serena's disappearance from the League of Nobles, Xavier married her sister Octa Butler. Through this union, Xavier became the patron of both the Butler and the Harkonnen families. The couple bore three daughters together, the youngest of whom went on the be the genesis of House Corrino.
Later Years
Xavier became a Primero in the newly-formed Army of the Jihad alongside Primero Vorian Atreides, and the two became firm friends, in part because of their contraasting styles of leadership and strategy.
Xavier was credited with the contentious idea of bombarding Earth with atomics, an action that not only desroyed the then Omnius Prime, but also obliterated all life on the planet.
Death and Legacy
Xavier later spent his life in a successful effort to kill Grand Patriarch Iblis Ginjo. Jihad records of the time indicate that Iblis was revered as a martyr and Xavier was marked as a traitor. As a result, the Harkonnen name became tarnished and Xavier's descendants adopted the surname Butler. Xavier's grandson, Abulurd, later ressurected the name after learning an alternate account from Vorian Atreides, much to the dismay of both his family and the League in general.
In an ironic twist, each and every Padishah Emperor ever to rule humanity has been a straight line-descendant of Xavier Harkonnen, the man who is seen as one of history's great traitors.
Behind the Scenes
Xavier Harkonnen is a principle character in the non-canon prequel 'Legends of Dune' trilogy by Brian Herbert and Kevin J. Anderson.