Normally, a strong Think Tank has 20 resident or part-time researchers, has a board of notables, closely monitors an aspect of society with periodic data and statistics, produces reports and diagnoses from time to time.
The answer to “who are the best experts on X subject” should be a Think Tank, not a single individual. We use this definition in choosing what we consider to be an almost Think Tank.
A Think Tank should also be a source of human resources for government positions, with the assurance that they will have a place to return when the government in question ends.
The private sector public sector exchange that this structure offers is extremely beneficial for both.