Shakkad the Wise was one of the rulers of the Old Empire.
He had remarked on the rejuvenating properties of the obscure spice melange discovered by the chemist Yanshuph Ashkoko and there had been a small market for the natural substance among offworlders at the Arrakis City spaceport.
Behind the Scenes
Shakkad is mentioned once in CoD as a ruler. However in the narrative of TBJ, he is mentioned as an Imperial chemist, clearly hinting at the Old Imperial era.
It is possible that the authors of TBJ confused the names of Shakkad and Ashkoko.