800-pound gorilla -> κυρίαρχος, απειλή
(idiomatic) An entity that dominates its environment.
(idiomatic) Something dangerous, menacing, or spooky that is obvious but not addressed.
The weight in the metaphor can be varied quantitatively.
Occasionally other nouns are substituted, most commonly elephant from another idiom, but also more context-specific nouns, such as rutabaga in an article on gardening.
Occasionally adjectives are inserted to modify gorilla to bring the metaphor closer to the context.https://en.wiktionary.org/wiki/800-pound_gorilla