Who is who is a flexible phrase that can mean a few related things, depending on how it’s used.

Core meaning

At its simplest, “who is who” (often written as “who’s who”) is about identity.

You use it when you’re trying to sort out which person is which in a group, or when you want to understand people’s roles or importance.

Example: “I’ve just joined this company and I’m still figuring out who is who in the office.”

Here it means: learning names, positions, and how everyone fits together.

The phrase “who’s who”

“Who’s who” is a set expression with two common senses:

  • Knowing identities and roles
    • “After a few weeks in town, we finally knew who was who.”
  • A list of notable people
    • A “who’s who of tech leaders” means a group that includes all the key or famous people in that field.

Dictionaries define “who’s who” as either information about each person in a group or a lineup/list of important figures.

Language angle: “who” itself

The word “who” is an interrogative and relative pronoun used for people:

  • To ask questions: “Who are you?”, “Who did this?”
  • To link extra info to a noun: “The person who called you left a message.”

“Who is who” basically doubles that idea: we’re not just asking about one person, but about how each person in a set is identified or ranked.

In forums and memes

Online, “who is who” and especially “who’s who” often show up as jokes or wordplay.

  • People riff on the classic Abbott and Costello “Who’s on First?” routine, turning “who is who” into a playful back‑and‑forth of confusion.
  • Meme titles like “who’s who’s who” stack the phrase just for the absurdity.

In those settings, the phrase keeps its identity-confusion core, but it’s exaggerated for humor.

TL;DR:
“Who is who” (or “who’s who”) is about figuring out identities and roles in a group, and by extension can mean a lineup of the most notable or important people in some field.

Information gathered from public forums or data available on the internet and portrayed here.