Rastic, take a look at the Tips for this lesson.
In English, the one word "who" can be used as an interrogative pronoun, an object pronoun, and a relative pronoun:
1. Who is the man standing next to my wife? [interrogative]
2. The man who is standing next to my wife is my brother. [relative]
3. The musician who(m) I am listening to is a famous rock star.
In Dutch, the who in 1 and 3 is a different word from the who in 2 (wie vs. die).