Longman Dictionary of Contemporary English
backroom boy
noun
EXAMPLES FROM CORPUS
▪ 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.
Wiktionary
backroom boy
n. (context chiefly British English) Someone who has an anonymous support role in an organization, especially a technician or scientist; a boffin.
WordNet
backroom boy
n. an expert adviser involved in making important decisions but usually lacking official status [syn: brain truster]