senior advisor; chief advisor
A high-ranking advisory position in an organization, often an honorary or senior role given to experienced individuals.
He was appointed senior advisor to the company.
As a senior advisor, he provides advice drawing on his many years of experience.
顧問 is a general advisor, while 最高顧問 is the highest-ranking or most senior advisor.
Compound of 最高 (highest) and 顧問 (advisor).