Advisor was the coveted sixth and last of the rank of the Mentat order. Only 1/20 of the novices achieved it.
Advisors were skilled in wisdom and diplomacy, possessing the abilities of all the lower ranks but also with sophistication and understanding. One Advisor was equal in price and value of a Sardaukar legion or a bloc of CHOAM shares.
Advisors planned for the long run, and negotiated delicate matters they judged matters of life and death. Regularly, a field marshal, a planetary governor, or a CHOAM director would closet himself with an Advisor before taking key actions. A Mentat-Advisor was thought to be able to transform a mediocre ruler into a respected leader, and a better than-average ruler into a potential emperor.
By the 9000s, no Great House lacked a Mentat-Advisor. A House should frame, purchase, brief and function a suitable Advisor and several years would pass. Not only were Advisors sometimes unavailable, but long waiting lists and astronomic bidding might further delay re placement. For this reason the loss or death of an Advisor was often disastrous to a House's fortunes.