Who is the official narrator of Star Wars? I.e., who is the one saying "A long long time ago, in a galaxy far far away?"
According to How Star Wars Conquered the Universe, it is none other than R2-D2 himself. The book quotes George Lucas as saying:
“The entire story of Star Wars is actually being recounted to the keeper of the Journal of the Whills—remember that?—a hundred years after the events of Return of the Jedi by none other than R2-D2.” Source
The Star Wars: Episode I - The Phantom Menace: Read-Along Story Book-and-Record was narrated by an unnamed member of the Jedi Council. Interestingly, he starts the narration with...
"A LONG TIME AGO IN A GALAXY FAR, FAR AWAY . . ."
...despite the fact that he, presumably, lives in the Galaxy at the time of the events in question.
"We, the members of the Jedi Council, have created this record of those terrible events. This recording device has captured the images and sounds of the struggle so that future generations will remember".
In the Disney canon, the Whills write down the Journal of the Whills. Among other things it contains the narration, including "a long time ago in a galaxy far, far away..." and the Episode IV intro crawl. There is no indication that R2-D2 played a role in recounting the story.
This is detailed in the short story Whills. Excerpt from Wookieepedia:
An unidentified Whill opens with the exposition "a long time ago in a galaxy far, far away..."
According to the Galaxy Guide 1: A New Hope Rebel-aligned historian Lt. Voren Na'al conducted a series of interviews with the various characters with whom Luke, Leia and Han interacted immediately before and during the Battle of Yavin.
A New Hope (or at least the historical work upon which the film was based) was based on his writings and the implication is that he also wrote the opening scroll since it's quoted in the text.
To: Major Arhurl Hextrophon, Executive Secretary and Master Historian, Alliance High Command
From: Lieutenant Voren Na'al, Assistant Historian
Regarding: Research into the events immediately preceding the Alliance victory at the Battle of Yavin.
Sir: Your notes regarding the events surrounding the Alliance victory at Yavin (for inclusion in the upcoming Official History of the Rebellion, Volume One) are indeed woefully incomplete, as you had predicted.
The final battle is fully documented in the Yavin base computer banks. But the strange tale of the great heroes of the Alliance, namely Commander Skywalker and his associate, remains something of a mystery to most of the support personnel — myself included. When you assigned me the task of backtracking their adventures from Tatooine to Yavin, 1 hoped initially to shed new light on the deeds and accomplishments of the heroes, perhaps making them appear a little more "human" than we have been led to believe.
Please forgive my enthusiasm for these fine beings, Major Hextrophon, and excuse the blatant unprofessionalism of the enclosed report. Where and how you choose to use this wealth of information is, of course, up to you. I just hope that I have added some small amount of knowledge about these strange and dangerous times in which we live.
A Long Time Ago....
To: Arhul Hextrophon
From: Voren Na'al
Subject: The Yavin Report
Looking back on my research over these past weeks, I am struck by a certain feeling of accomplishment. If anything. I feel the vast number of contacts I've made and the sheer volume of background information I have gathered for this report should make the Alliance auditors feel their credits were well spent.
As I go over my notes, I hit upon the obvious. The focus of this report is not the events themselves, epic though they may be, but rather the many diverse beings that played out the tale. It is said that moments of bravery are most often created by moments of necessity. This story defies that notion, it is far easier to succumb to tyranny than to fight it, for freedom is not a necessity, it is a gift. Those who recognize its worth fight to protect it.