Who is Reverend Mother Bellonda from Chapterhouse: Dune and what is their importance?

Reverend Mother Bellonda is old, fat, florid, and perpetually scowling, "Bell" is Mentat-Archivist, who resents opulence and frivolity when the Honored Matres are hunting the Bene Gesserit Sisterhood. Bell feasts on violence and has to be restrained. Having long argued that the Mentat ghola Duncan Idaho is dangerous - perhaps a Kwisatz Haderach - Bell, when left off an inspection tour, hurries to his no-ship prison, intending to find a valid excuse for killing him. She cannot see how Reverend Mother Superior Darwi Odrade fails to see his danger, when he even flaunts his clear mind and admits he influences her decisions. When Odrade goes on a suicide mission to Junction to meet with the Grand Honored Matre, Bell is left on Chapterhouse.