As Jeaein said above, "누가" is short for "누구+가(subject particle)" meaning it's a subject, but the pronoun "누구" can be a subject like "누가", object, topic or predicate in a sentence. e.g. 누가(=누구가) ☞ as a subject 누구 + 는 ☞ as a topic 누구 + 를 ☞ as an object 누구 + 예요 ☞ as a predicate 누구 + 의 ☞ as a possessive 누구 + 에게 ☞ to who(m) \^o^/

누구 +가 = 누가 누가 is the short form of 누구 가

I think this is really helpful if you want to understand when to use 누가 vs 누구. If you don't want to listen for so long, just click the PDF! :) http://www.talktomeinkorean.com/lessons/l1l23/ Summary: 누가 is just 누구 plus 가. The subject marker 가 is added when you are emphasizing 'who' as the subject of an action or state.

누가's "누" is old say "누구"