backroom boys

US /ˈbæk.ruːm bɔɪz/
UK /ˈbæk.ruːm bɔɪz/
"backroom boys" picture
1.

people who do important work but have no contact with the public

:
The success of the campaign was largely due to the hard work of the backroom boys.
The scientists working on the secret project were the real backroom boys.