the back-room boys
Someone who advises a public figure or maintains a professional role that does not garner public attention. Originally used to describe scientists and technicians who worked without public knowledge or recognition in the United Kingdom during World War II. Primarily heard in UK. Although he is a skilled political strategist, he lacks the charm and charisma necessary to run for office himself and, therefore, is likely to stay a backroom boy for the rest of his career.
the ˈback-room boys(British English) scientists, researchers, etc. who do important work but do not have direct contact with the public: It’s thanks to the back-room boys more than to the sales team that the product is such a success.
See also: boy