who

Used in direct and indirect questions to ask which person or people.

• Who is that man next to your sister?
  Kız kardeşinin yanındaki adam kim?
• Do you know who called me last night?
  Dün gece beni kimin aradığını biliyor musun?

Used as the object of a verb or preposition, especially in questions, instead of whom.

• Who did you invite to the party?
  Partiye kimi davet ettin?
• Who are you talking to on the phone?
  Telefonda kiminle konuşuyorsun?

Used to begin a clause that says which person you mean or adds information about someone.

• He's the friend who lives next door.
  O, yan dairede oturan arkadaşım.
• My brother, who lives in Ankara, is a doctor.
  Ankara'da yaşayan ağabeyim doktor.