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.