"800-pound gorilla" is an American English expression for a person or organization so powerful that it can act without regard to the rights of others or the law. The phrase is rooted in a joke riddle:
"Where does an 800-lb. gorilla sit?"
The answer:
"Anywhere it wants to."
This highlights the disparity of power between the "800-lb. gorilla" and everything else.
The term can describe a powerful geopolitical and military force, or, in business, a powerful corporate entity that has such a large majority percentage of whatever market they compete within that they can use that strength to crush would-be competitors. (The metaphor includes an inherent bit of hyperbole; the highest weight yet recorded for an actual obese gorilla is 600 lb. (270 kg). The average weight is 400 lb.)
The metaphor has been mixed, on occasion, with the metaphor of the elephant in the room.