Wellington Yueh

Dr. Wellington Yueh was a Suk doctor and a sleeper agent of Baron Vladimir Harkonnen who served House Atreides as the personal physician of Duke Leto Atreides I. Trusted above suspicion because of the Imperial Conditioning all Suk graduates carried, he engineered the betrayal that brought down the House on Arrakis, and was himself discarded once his treachery had served the Baron's ends. (Dune)

A Suk physician and his conditioning#

Yueh was a graduate of the Suk School and had married the Bene Gesserit Sister Wanna. Graduates of the Suk High College bore on their foreheads the diamond tattoo of Imperial Conditioning, a process held to make it psychologically impossible for them to take a human life or even to contemplate such an act. So absolute was the reputation of that conditioning that no one in the Imperium suspected a Suk doctor of treachery, and it was precisely this trust that the Harkonnens set out to exploit. (Dune)

The Baron's Twisted Mentat, Piter de Vries, achieved what was believed impossible without killing the subject: a breakthrough in breaking a Suk's conditioning. The Harkonnens took Wanna and forced Yueh to witness her brutal torture in the Mentat's pain amplifiers. Yueh's grief and hatred grew until he harbored murderous intent toward her tormenters and anyone who stood in his way, a burning psychosis that overrode the inhibitors his conditioning had placed in him. (Dune)

The bargain#

Informed that the doctor had become pliable, the Baron promised Yueh his wife's freedom in exchange for the Duke and his family. Yueh saw the offer as his one chance at revenge. He judged that Wanna was very likely already dead, but he had to be certain her suffering was ended, and the bargain gave him the means to strike at the Harkonnens through the Duke he was about to betray. (Dune)

The plot also depended on misdirection. Harkonnen agents fed false evidence to the Duke's Mentat and Master of Assassins, Thufir Hawat, steering his suspicion toward the Duke's concubine, Lady Jessica. Hawat saw no reason to test Yueh, trusting in the High College's conditioning. Jessica, herself working to clear the household of suspects through her powers of observation and Truthsaying, cited the hatred she and the doctor shared for House Harkonnen over the murder of his Bene Gesserit wife. The doctor's loyalty was never seriously questioned. (Dune)

The fall of Arrakeen#

Weeks after House Atreides arrived on Arrakis to take over spice production, the House was ambushed in the night by Harkonnen legions and the Emperor's own Sardaukar. Yueh played his part. After killing the Fremen housekeeper Shadout Mapes in the Arrakeen residence, he sabotaged the residence's main shield generator and left the compound exposed to the attackers. He then disabled Duke Leto with a tranquilizer dart, lamenting his betrayal and assuring the Duke that Paul and Jessica would be kept safe. (Dune)

Before the Duke was taken, Yueh replaced one of Leto's teeth with a hollow false tooth containing a scanner-proof core. Inside was a capsule of poison gas. Leto was brought before the Baron and Piter de Vries as a bound and helpless prisoner, carrying the means of his revenge in his own mouth. (Dune)

Death and the keeping of a promise#

When Yueh saw the Baron, he understood from his manner that Wanna was long dead and no longer of use as a hostage. With that knowledge, and with the weapon already planted in the Duke, he resigned himself to his fate. He gave the Baron a cryptic warning of his coming death, and Piter de Vries killed him on the Baron's order. (Dune)

Yueh kept his word to the Duke. He had already arranged the escape of Paul and Jessica into the deep desert, leaving them a Fremkit that held Leto's ducal signet ring and a note from Yueh. When the Baron prepared to have Leto tortured for the whereabouts of his family, the Duke crushed the false tooth and filled the room with poison gas. The Baron barely escaped, but everyone else present died, including Piter de Vries. The doctor's main target survived, yet Yueh had still slain the man who kidnapped, tortured, and murdered his wife, and had guaranteed the survival of his Duke's family. (Dune)

He was a gaunt man dressed in loose black clothing, with a square block of a head and black hair gathered in a silver Suk ring at his left shoulder, an aged complexion, angled cheeks, dark almond eyes, and a drooping mustache over purpled lips, his forehead marked with the diamond of Imperial Conditioning. (Dune)