A Who’s Who is a book or list containing the names and biographies of famous or noteworthy people. For example, the British publication Who’s Who is published annually and contains information about some 30,000 notable Britons. As an idiom—usually within the phrase a Who’s Who of—the term is usually used to describe something that involves many noteworthy people.
Who’s Who should be capitalized as a proper noun, but many publications don’t bother. Likewise, it would make sense to italicize the term (because we usually italicize the titles of books), but most writers don’t do so. The uncapitalized who’s who is more common than Who’s Who, which suggests that most writers and editors don’t consider it incorrect. Meanwhile, there’s no reason Who’s Who should be hyphenated or placed in quotation marks.
His list of conquests reads like a Who’s Who of the world’s most beautiful women. [Daily Mail]
The list includes dozens of household names, reading like a Who’s Who of the Egyptian sports and entertainment industries. [Montreal Gazette]
Only a Who’s Who of our respected and biggest financial institutions: Bank of America, Citigroup, JP Morgan Chase, Wells Fargo and Ally Financial. [Chicago Sun-Times]