Who is the speaker of The Prologue in Act I of Romeo and Juliet?

The chorus acts as a narrator. You will find the chorus
only at work before the first Act and in the beginning of the
second.

During Shakespeare's time, when plays were
performed on the new stage of the Globe Theater, props and special effects were very
minimal. The Prologue served that purpose of filling in the blanks ahead of time so that
when the actual play began and got underway, audience members could refer back in their
memory to the introductory material they heard.

The chorus
gave a sort of road map to the audience for what was about to
happen.

You could also argue that the chorus' speaking
parts are Shakespeare's opportunity to talk directly to his audience about what was
going on.