Gaius Helen Mohiam is a fictional character in the Dune universe created by Frank Herbert. She is a Bene Gesserit Reverend Mother, and initially appears in the 1965 novel Dune and its 1969 sequel, Dune Messiah. Mohiam also has a major role in the Prelude to Dune prequel trilogy (1999–2001) and the Caladan Trilogy (2020–2022) by Brian Herbert and Kevin J. Anderson. In Dune, Gaius Helen Mohiam is the Imperial Truthsayer, and the mentor of Lady Jessica, the Bene Gesserit concubine of Duke Leto Atreides. Mohiam is interested in Jessica's young son Paul Atreides, who is a key figure in the Bene Gesserit breeding program but has also displayed unusual potential. She ultimately loses any influence she may have had over Jessica or Paul, who ally themselves with the native Fremen of Arrakis and depose Padishah Emperor Shaddam IV. In Dune Messiah, Mohiam joins a conspiracy to remove Paul from power, which fails. Gaius Helen Mohiam is portrayed by Siân Phillips in David Lynch's 1984 film Dune, by Zuzana Geislerová in the 2000 miniseries Frank Herbert's Dune and its 2003 sequel Frank Herbert's Children of Dune, and by Charlotte Rampling in the 2021 Denis Villeneuve film Dune and its 2023 sequel. Description In the novel Dune, the Baron Vladimir Harkonnen has this impression of Gaius Helen Mohiam: In Dune Messiah, Herbert notes that Mohiam's eyes are "dark with the blue brilliance of her melange addiction." Novelist Brian Herbert, Frank Herbert's son and biographer, describes Mohiam as "a witch mother archetype". The non-canon Dune Encyclopedia (1984) by Willis E. McNelly gives an extensive, alternate biography for Mohiam, including the first suggestion that she is Lady Jessica's mother. Appearances Dune As Dune begins, the "old crone" Reverend Mother Mohiam comes to Caladan to "test" young Paul Atreides before his departure for Arrakis. Having trained Paul's mother Lady Jessica at the Bene Gesserit school on Wallach IX decades before, Mohiam now holds a lethal gom jabbar to Paul's neck. If he withdraws his hand from a box that inflicts pain through direct nerve induction, the gom jabbar will kill him instantly. Mohiam explains to Paul that the purpose of the test is to discover whether Paul is "truly human", by requiring him to endure pain and still act rationally. He passes the test, and Mohiam (though still furious over Jessica's choice to disobey the Sisterhood and bear a son instead of a daughter)