Who is Duncan Idaho from Heretics of Dune and what is their importance?

Duncan Idaho is a "ghola" reincarnation of the great sword master of House Atreides in the original Dune, 3,500 years ago, Duncan begins this novel as a 12-year-old boy being physically trained under the direction of the renowned Bashar Miles Teg. The Bene Gesserit Sisterhood, which has commissioned eleven previous Duncan gholas from the Bene Tleilaxu, is guarding this one heavily. The predecessors have all been killed before an Imprinter could bring back their pre-ghola memories.