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) by Brian Herbert and Kevin J. Anderson.
Mohiam is portrayed by Siân Phillips in David Lynch's 1984 film Dune, and by Zuzana Geislerová in the 2000 miniseries Frank Herbert's Dune and its 2003 sequel Frank Herbert's Children of Dune.
In the novel Dune, the Baron Vladimir Harkonnen has this impression of Mohiam:
An old woman in a black aba robe with hood drawn down over her forehead detached herself from the Emperor's suite, took up station behind the throne, one scrawny hand resting on the quartz back. Her face peered out of the hood like a witch caricature — sunken cheeks and eyes, an overlong nose, skin mottled and with protruding veins.
The Baron stilled his trembling at sight of her. The presence of the Reverend Mother Gaius Helen Mohiam, the Emperor's Truthsayer, betrayed the importance of this audience.
In Dune Messiah, Herbert notes that Mohiam's eyes are "dark with the blue brilliance of her melange addiction."
The non-canon Dune Encyclopedia (1984) by Willis E. McNelly invents an extensive, alternate biography for Mohiam.
Read more about Gaius Helen Mohiam: Dune, Dune Messiah, Prelude To Dune