Unlike his descendant Vladimir Harkonnen, Xavier was noble in nature, courageous, and possessed unshakable integrity. In the series, Xavier Harkonnen was born to wealthy nobles, Ulf and Katarina Harkonnen. At the age of six, Xavier's parents were killed by thinking machines, and he was later adopted by Emil and Lucille Tantor. He received a military commission at age 19.
Xavier courted Serena Butler, daughter of viceroy Manion Butler, and fathered her son Manion, who was killed by thinking machines in an act which incited the jihad. Manion the Innocent was revered as a martyr.
and later, Priestess of the Jihad
Xavier was credited for the strategy which overcame the cymek attack on Salusa Secundus, after which he was awarded the rank of Tercero First Grade. During the attack, he ordered all of the military units to fall back and protect the planentary shield generators which caused much of Zimia to be destroyed. At first many units disregard his orders, but evenutally they fell back.
Eventually he orchestrated the destruction of the cymeks by picking them off one at a time. After eight of thirty cymeks have been destroyed, the others retreated, leaving Zimia in ruin, but the planet secure.
After Serena's disappearance from the League of Nobles, Xavier married Octa Butler. Through this union, Xavier became the patron of both House Butler and House Harkonnen. At the start of the Jihad, it was Xavier's idea to bombard Earth with a massive nuclear strike, destroying the primary stronghold of Omnius.
Xavier became a Primero (general) in the Army of the Jihad alongside Vorian Atreides; while the two initially were rivals for Serena Butler's love, they eventually became good friends and battle comrades. For most of his career, Xavier was highly regarded as one of humanity's champions. Xavier later sacrificed his life and his reputation in order to eliminate the corrupt Grand Patriarch of the Jihad, Iblis Ginjo. However, it was Iblis who came to be revered as a martyr while Xavier was marked as a traitor.
The Harkonnen name became tarnished and Xavier's descendants adopted the surname, Butler. It was Xavier's grandson, Abulurd, who after learning the truth from Vorian, decided to revive the Harkonnen name and, to the dismay of the League and the disapproval of his father, Quentin Butler, he changed his name to Abulurd Harkonnen.