De Vries had been trained as a Twisted Mentat by the Bene Tleilax; Vladimir Harkonnen did not want a mere data-processing human, but a calculating and clever man with corrupt imagination in order to assist him.
Mohiam and the BaronEdit
The Mentat welcomed Gaius Helen Mohiam and her assemblage to Harkonnen Keep on Giedi Prime. Mohiam threatened the reluctant Baron with revealing his secret spice stockpile from Arrakis to the Emperor. When the Baron told him that Mohiam sought him to impregnate her for the Bene Gesserit's own ends, De Vries suggested that the safest way was to comply with her.
Kidnapping of Paul AtreidesEdit
After Piter kidnapped the newborn Paul Atreides inside the Imperial Palace on Kaitain; he was cornered by the Emperor's wife, the Lady Anirul Corrino. As Anirul convulsed with an overwhleming experience of Other Memory, Piter then found himself in a life and death situation with Mohiam, who had been present at Jessica's delivery of her child. De Vries was quickly dispatched Mohiam, and Paul was safely returned to his newly arrived father, Duke Leto I, who had just come from Caladan. After the corpse of de Vries was presented to Vladimir Harkonnen, the Baron decided to request another de Vries to be grown from the axolotl tanks.
Breaking Dr YuehEdit
A devious, cunning individual, de Vries was responsible for discovering how to break the Imperial Conditioning of a Suk doctor of never taking a life. He discovered that if he held a loved one of the Suk doctors to ransom, he could control their behaviour any way he wished. This was demonstrated by the betrayal of House Atreides by Dr. Wellington Yueh. De Vries had kidnapped Yueh's wife, murdered her, and convinced Yueh that she was still alive. De Vries had promised that he would return his wife to him if he were to do the Harkonnens' bidding. This effectively broke Yueh's Imperial Conditioning, and lead to the death of Duke Leto Atreides.
Ghola Death on ArrakisEdit
De Vries was killed by Leto when he mistakenly perceived de Vries to be the Baron Harkonnen. In a drugged state, Leto bit down on a poison gas tooth imbedded in his head by Yueh just before Leto was captured during the invasion of Arrakis. The Baron narrowly escaped, but de Vries was killed. In this way, Yueh managed to exact vengeance on the man that killed his wife.
Elimination of the Ghola LineEdit
After the Ascension of House Atreides, the Tleilaxu invited the exiled Count Hasimir Fenring to witness the testing of a new lethal nerve gas that the race had developed. In a laboratory in Thalidei, the Count witnessed the testing of the gas on the last remaining gholas of Piter. The Tleilaxu Master who tested the gas lamented that since House Harkonnen was destroyed on few years earlier, that the de Vries gholas will never be ordered again.