During the reign of Emperor Paul Atreides and his son Leto Atreides II, numerous gholas of Duncan Idaho were created by the Bene Tleilax, either at the request of House Atreides or as an unexpected gift to them.
Origin of the Duncan Idaho Ghola
The original ghola, named Hayt before reclaiming his original name, was presented as a gift to Paul Atreides, with the intention of assassinating the Emperor after the death of his concubine Chani. However, after the cellular memories of the original Duncan Idaho arose and prevented the ghola from completing that task, he became a trusted servant of Paul, and later the lover of Paul's sister Alia.
The reawakening of the memories of Duncan Idaho proved to be pivotal, not least for the Bene Tleilax, who had been attempting to accomplish such a feat for thousands of years without success. Subsequently they continued to create numerous more gholas over the following millennia.
Variances between gholas
Each was unique, exhibiting differences in training, conditioning, and disposition. Such changes varied depending on the mood and ambition of the Tleilaxu at the time of their creation.
The demand for Duncan Idaho gholas remained after the ascendancy of Leto Atreides II, the God-Emperor. Leto II relied heavily on a succession of Duncan Idaho gholas to fulfill his Golden Path, while the Bene Tleilax willingly supplied them in the hope of destroying the powerful God-Emperor through deception and subterfuge.
Successive gholas were often based on the genetic material of a previous Idaho ghola, rather than the original Duncan Idaho. This led to a sporadic accumulation of memories and experiences, but also provided a genetic throwback through which new traits of the Atreides line could be plucked or refined.
Gholas After Leto II's Death
After the death of Leto II, the Idaho gholas endured, mainly through the efforts of the Bene Gesserit who slowly realized the value of Idaho's genes for their own political ends. Ultimately it was an Idaho ghola who discovered a way of resisting the sexual enslavement tactics employed by the Honored Matres, and thus assisted the Bene Gesserit in their partial victory of their Scattering rivals.
After the merger of the Honored Matres and the Bene Gesserit, this particular Duncan Idaho ghola left to join the scattering led by Sheeana.
Behind the Scenes
At least one Duncan Idaho ghola features in every novel from Dune Messiah through Sandworms of Dune. Every Duncan ghola actually featured in the books does manage to "awake" and remember the life of the original Duncan Idaho, except the last ghola, who became the ultimate Kwisatz Haderach. The last Idaho ghola remembered the lives of all previous incarnations after being mutually imprinted to Murbella.