Italian relative pronouns (pronomi relativi) are called as such because, in addition to substituting for the noun, connect (relate) two clauses. The clause introduced by the pronoun is subordinate and is dependent on the main clause.
È molto bello il vestito che hai acquistato.
The dress that you bought is very nice.
The relative pronouns are: chi, che, cui, and il quale.
- chi is invariable, is used in the masculine and feminine singular, and refers only to a person:
Chi rompe, paga.
He who breaks (it), pays (for it).
Chi tra voi ragazze vuole partecipare alla gara, si iscriva.
Those of you girls who want to participate in the competition, sign up.
In general, chi functions as subject and object; in fact, it corresponds to a relative pronoun preceded by a demonstrative.
Non mi piace chi non lavora seriamente.
I do not like those that do not work seriously.
Sometimes chi functions as an indirect complement if preceded by a preposition.
Mi rivolge a chi parla senza pensare.
I was referring to those who speak without thinking.