eight-hundred-pound gorillaor 800-pound gorilla
1. A person or organization regarded as being extremely powerful, aggressive, or intimidating.
2. An obvious or major problem that people are too afraid or embarrassed to talk about.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.