who's who

(countable, sometimes capitalized) A publication containing biographies of well-known or important people.

(countable) A list of notable, famous, or upper-class people.

(uncountable) Collectively, the elite class.

(countable) A person appearing in a Who's Who publication.

(countable) A celebrity or famous person, someone likely to be in such a publication.

(uncountable, idiomatic) The identities of specific people, understood in terms of such distinguishing characteristics as their backgrounds, prominence, achievements, jobs, etc., as a basis for comparing them and especially as a basis for ranking them within a social group.