dyed-in-the-wool

US /ˌdaɪd.ɪn.ðəˈwʊl/
UK /ˌdaɪd.ɪn.ðəˈwʊl/
"dyed-in-the-wool" picture
1.

pur et dur, invétéré

having very strong beliefs, opinions, or habits that are not likely to change

:
He's a dyed-in-the-wool conservative.
C'est un conservateur pur et dur.
She's a dyed-in-the-wool optimist, always seeing the bright side.
C'est une optimiste pure et dure, voyant toujours le bon côté des choses.