From Longman Dictionary of Contemporary Englishbackroom boyback‧room boy /ˈbækrʊm ˌbɔɪ, -ruːm-/ noun [countable usually plural] British English informal BOHsomeone such as an engineer or scientist whose work is important but who does not get much attention or fame
Examples from the Corpus
backroom boy• Poor eyesight had prevented Thomas from qualifying as a pilot; but he was not content to be a backroom boy.• Reg was already a well respected backroom boy and came to the club from highflying Walborough Solid Fuel Albion. 