Wah How to use "It was...who"

We can use It was...who to answer the questions which asks about the person.

    A: Who was the first person to discover America?
    B: It was Christopher Columbus who first discovered America.

    A: Who do you know who works for the Perry company?
    B: It was Martin who works for the Perry company.

    A: Who wrote Harry Potter?
    B: It was J. K. Rowling who wrote Harry Potter.

    A: Who founded Apple company?
    B: It was Steve Jobs who founded Apple company.

    A: Who was the first James Bond?
    B: It was Sean Connery who was the first James Bond.

Note : It was him who did it  "It was he who did it" because He did it not Him did it.

It was Taylor Swift who sings Love Story.

Wah How to use relative pronouns (Who, Whom, Which, That).

Who, Whom, Which, That are the relative pronouns.
A relative pronoun is a pronoun that introduces a relative clause.

1. Who (as subject)
We use who referring to people.
    The person who went out with me last night is my old friend.
    Annie is the girl who get this job.
    Martin, who is an English teacher, comes from New York.
    Julio, who is very kind, is my colleague.

2. Whom (as object)
We use whom referring to people.
    The person whom I spoke to was my father.
    James, whom I went to school with.
    Annie, whom I like so much, is my English teacher.
    This is Helen, whom you met at the party last week.
    The man whom you told me about went to Rome last week.