Feyd Rautha Harkonnen was the youngest nephew of the Baron Vladimir Harkonnen, and brother to Glossu Rabban. Later pronounced heir designate to the Harkonnen barony and therefore "Na-Baron". Immediately after the Fremen uprising on Dune Feyd-Rautha challenged Paul Atreides to a duel in which Feyd-Rautha was killed.
Dark-haired Feyd was as lean and muscular as the Baron was morbidly obese; the Baron also remarks that the "full and pouting look" of Feyd's lips is "the Harkonnen genetic marker."
Part of House Harkonnen, and brother of "The Beast" Rabban Harkonnen, Feyd was the son of Abulurd Harkonnen, Vladimir Harkonnen's half brother, who renounced the Harkonnen name and all rights to the title when given the subdistrict governorship of Rabban-Lankiveil, and Emmi Rabban. Grandson of Dmitri Harkonnen.
In the books
Prelude to Dune
In the Prelude to Dune prequel trilogy by Brian Herbert and Kevin J. Anderson, it is established that Feyd had been born on the Harkonnen planet Lankiveil as the second son of Vladimir's younger half-brother Abulurd Harkonnen and his wife Emmi. The Bene Gesserit, desiring a son by Abulurd for their breeding program but finding Glossu unacceptable, secretly administer fertility drugs to an aging Emmi, who soon conceives Feyd.
Named after his maternal grandfather, Rautha Rabban, who had been murdered by Glossu, Feyd becomes honorable Abulurd's hope for a son who would not have to inherit the dishonor of the name Harkonnen, and a worthy heir in comparison to his older, murderous son, Glossu. The Baron decides to take the infant Feyd from his father to raise on the Harkonnen homeworld Giedi Prime as another possible heir for himself, and as punishment for Abulurd's attempts to sever all his ties to House Harkonnen. In time, the Baron comes to favor Feyd over Glossu.
As Dune begins, Feyd-Rautha figures heavily in the Baron's plans to gain power for House Harkonnen. The Baron favors the handsome and charismatic Feyd over Feyd's older brother Glossu Rabban ("The Beast") because of Feyd's extreme intelligence and his dedication to the Harkonnen culture of carefully-planned and subtly executed sadism and cruelty, as opposed to Rabban's outright brutality.
The Baron could see the path ahead of him. One day, a Harkonnen would be Emperor. Not himself, and no spawn of his loins. But a Harkonnen. Not this Rabban he'd summoned, of course. But Rabban's younger brother, young Feyd-Rautha. There was a sharpness to the boy that the Baron enjoyed ... a ferocity ... A year or two more — say, by the time he's seventeen, I'll know for certain whether he's the tool that House Harkonnen requires to gain the throne.
Feyd is, for a while, the Baron's heir, or na-Baron. To assure Feyd's power, the Baron intends to install him as ruler of Arrakis after a period of tyrannical misrule by Rabban, making Feyd appear to be the savior of the people.
Feyd, like Paul Atreides, is also the product of a centuries-long breeding program organized by the Bene Gesserit, who planned their own alliance by joining a Harkonnen son to an Atreides daughter with the expectation that their offspring would have a high probability of being their hoped-for Kwisatz Haderach. For this reason, Lady Jessica's decision to defy the Sisterhood and to produce an Atreides son, Paul, threw the Bene Gesserit's plans into turmoil and established an irreconcilable tension between Feyd and Paul as the scions of their bitterly opposed noble houses. The risk of one or both of these young men being killed, destroying thousands of years of genetic engineering, is so great that the Bene Gesserit send an envoy, Margot Fenring, to seduce Feyd and conceive a child, salvaging his genetic material.
And the Lady Fenring thought: Can that be the young man the Reverend Mother meant? Is that a bloodline we must preserve?'
Margot also intends to "plant deep in his deepest self the necessary prana-bindu phrases to bend him," which she later refers to as the "Hypno-ligation of that Feyd-Rautha's psyche." Presumably he is thus "prepared" and made vulnerable to a command which will cause complete muscle paralysis, a technique the Bene Gesserit sometimes use on individuals who are considered highly dangerous.<ref name="Dune"/> It is also later noted by the Reverend Mother Mohiam that Feyd's encounter with Lady Fenring produced a daughter.
Feyd's ambition and impatience to inherit the Baron's title and power spur him to attempt his uncle's assassination; as punishment for the failed attempt, the Baron forces Feyd to single-handedly slaughter all the female slaves who serve as his lovers. He explains that Feyd has to learn the price of failure.
As Paul makes his final bid to usurp the Padishah Emperor's power, he is challenged by Feyd, the current Harkonnen leader after the deaths of the Baron and Rabban. Though famed for his prowess in single combat, Feyd intends to guarantee victory by breaking the formal rules of kanly (which govern this type of challenge) and using a hidden poison spur in his fighting outfit. He nearly succeeds in killing Paul in the ritualized fight, as Paul struggles with whether to try the paralysis word-sound and owe the Bene Gesserit his victory, or to risk his life against Feyd in a "fair" fight. Paul manages to defeat Feyd without the command, and goes on to ascend the throne of the Emperor.