Learner's definition of WHO
1 a : what or which person or people — used when you do not know the name or identity of a person or group of people that you are talking about or asking about
b — used to question a person's character or authority
Who will be the next president?
Who is standing next to you in this photo?
I didn't know who he was.
Find out who they are.
I wonder who else signed up.
Who should walk in [=who do you think walked in] when we least expected it? My parents!
She isn't sure who she talked to.
c — used in questions that are meant to say that no one would or would not do something, know something, etc.
Who are they to tell us what to do? [=what makes them think they can tell us what to do?]
Who do you think you are? [=what gives you the right to say or do this?]
Who do you think you're talking to? [=what gives you the right to speak to me in this (rude) manner?]
They may come or not. Who cares? [=no one cares; I don't care]
Of course I would love to win a million dollars. Who wouldn't? [=anyone would]
“Are they coming?” “Who knows?” [=no one knows; I don't know]
Who are we kidding? [=we aren't kidding/fooling anyone]
2 — used after a noun or pronoun to show which group of people you are talking about
Subscribers who are interested in joining the discussion group should contact the secretary.
The people who conducted the study were extremely professional.
Someone who handles stress well will be more suited for the job.
I have a friend who my parents don't like.
3 — used to introduce an additional statement about someone who has already been mentioned
His patient, who was a well-known television personality, suffered a minor stroke.
The former president of the company, who is retired now, is credited with expanding and improving the product line.
Her uncle, who she's very fond of, lives next door.
orwho is who : information about the people who make up a group
We had lived in this town long enough to know who was who. [=to know the names of the different people, what they did, etc.]
I'm still learning who's who around the office.
2 a : a list of the names of the important and well-known people in a particular field b : the important and well-known people in a particular field