noun, masculine/mɔ̃s.tʁə sa.kʁe/plural: monstres sacrés
monstre sacré is masculine in French.
giant, celebrity (undisputed authority in a certain field)
“Je passai près d'une heure agréable avec lui mais Elsa s'ennuyait. Elle connaissait un ou deux monstres sacrés mais la technique ne l'intéressait pas.” — I spent nearly an hour in pleasant conversation with him, but Elsa was bored. She knew one or two big names [in theatre], but the technique did not interest her.
Literally, “holy monster”, used by Jean Cocteau to describe Sarah Bernhardt.