Expanded Dune
This article or section refers to elements from Expanded Dune.
Secondaries were monks that offered their lives to take care of the Cogitors.
The Cogitors, having no bodies, relied on Secondaries to be taken care of, to maintain their life support and electrafluid, to be transported etc. Secondaries were also the mediums through whom the Cogitors could interact.
It seems that each Cogitor was appointed one Secondary. For example Aquim was Arn Eklos' Secondary.