The Reverend Mother Gaius Helen Mohiam is perhaps the most powerful and influential living Bene Gesserit, (B.G.)  and is a remarkably intimidating presence in the novel. Her Bene Gesserit powers make her highly attuned to the thoughts, emotions, and actions of others, giving her a piercing, uncanny quality. Years of service to the B.G. and to ruthless political regimes have made her cold and practical, and she’s unsentimental about giving Paul the potentially fatal gom jabbar test. Additionally, the Reverend Mother is the Emperor Shaddam IV’s Truthsayer, meaning that she operates at the highest level of power. Having the Emperor’s ear, she can further the Bene Gesserit’s plans via her influence over the Emperor Shaddam’s decisions and strategies.

Despite her exceptional powers, the Reverend Mother is not infallible. Although Jessica trained under the Reverend Mother as her obedient student, she rebels against the Bene Gesserit’s demands when she bears the Duke Leto a son rather than a daughter. When Paul meets the Reverend Mother at age 15, he is already powerful enough to sense instances where she is lying or uncertain. This foreshadows that the Reverend Mother’s powers are not absolute, and that even a highly-trained Bene Gesserit can be bested by figures like Paul who have the optimal mix of genetics and training. Additionally, because the Reverend Mother is entirely devoted to the Bene Gesserit’s master plan, she becomes enraged and frightened when people – like Jessica – purposefully diverge from their prepared roles and destinies. She struggles to adapt to situations that are out of her control, or that conflict with the order that she is accustomed to.