Who is Mandell Gruber from Forward the Foundation and what is their importance?

Mandell Gruber is a gardner First Class, Gruber is content with his lot in life, having over the course of thirty years risen to his present rank. He is dismayed at the prospects of being appointed Chief Gardener, an office that precludes hands-on gardening. A native of the remote, wild planet Anacreon, Gruber is a bit younger than Hari Seldon when Hari serves as First Minister to Emperor Cleon I. They frequently meet in the garden and chat about the wonders of nature.