We use WHO with a subject. We use WHOM with an object. WHOM generally comes after a preposition. Using WHO and WHOM in english;
Whom do you love? I love Mary.
The person who phoned me last night is my mother.
Do you know the girl whom Samuel is talking?
My father is someone who loves cats.
Thanks to everybody who came here.
The man who you are waiting for.
Who has selected her for the finals?
My sister of whom her friend is jealous is very hardworking.