(For an answer to the actual question (i.e. why do we call him that), see below.)
I spot two possible factors for why the “R. R.” version of his name is a better choice:
1. It sounds better
Martin himself noted in an interview that as an author, your name is your brand, and therefore having a memorable and unique one like “George R. R. Martin” is ...
In this 2014 San Diego Comic Con panel discussion at 15m30s he says that his map of Westeros began as Ireland upside down, where the southwest of Ireland corresponds with the Fingers. The North definitely looks like the UK, with the Wall pretty much in the same place as Hadrian's Wall.
My Westeros began as upside down Ireland. You can see the Fingers is ...
George R. R. Martin has commented on this but surprisingly has stated that Westeros' shape is not based on the England and in fact can't even see the similarities himself. Although interestingly he does state that he based the fact that Westeros was off the west coast of Essos on UK being off the west coast of Europe.
Some readers have likened Westeros to ...
Because the convention is to use the name of authors as given.
George R. R. Martin gives his name on the cover of the book as George R. R. Martin so that is what you call him. Had he put George R. Martin we'd call him that, instead. If he'd chosen G. R. Richard Martin, we'd use that. I think the accepted answer has the probable reasons why he chose to use ...
According to this Q&A with his editor Anne Groell, GRRM foreshadows all the time as part of his "three-fold revelation strategy":
Q: Anne, although you're the envy of many a GRRM fan, do you ever wish you didn't have to edit the books so that you could be surprised by them all at once along with the rest of us?
A: No. As above, he doesn’t tell me ...
As TLP wrote, I'm not sure there are always three components, and not all events are foreshadowed. But there are many events that are foreshadowed over the course of the series. One memorable example is the Red Wedding, which is heavily foreshadowed:
Patchface sings about it in the prologue of ACOK:
Dany sees a vision in the House of the Undying:
Later in ...
Whilst it is incredibly unlikely that George would ever admit to doing this, especially whilst the show is still running, it is unlikely it is even a reference to that in the first place. The book appears to have first been mentioned in A Dance with Dragons and hinted at being poorly written then before the show went downhill.
The galley was ...
According to George R. R. Martin, this religion's dualistic aspects of a good and an evil god are inspired by Zoroastrianism, along with the Cathars of Medieval Europe.
In this interview (at about 47:00 GRRM) talks about his inspirations for religion in his works.
From the Wikipedia article on Zoroastrianism we can draw parallels to R'hollor.
The two young Walders Frey at Winterfell play a game called King of the Crossing in which the King must hold to an oath unless he slips in the word "mayhaps" unnoticed. If you look at the interaction between Lord Frey and Robb & Catelyn right before the Red Wedding, Frey does just that- slips in a "mayhaps" when the Starks ask for food. Thus, it's not ...
There already is a rather famous George Martin, also known as "the fifth Beatle". There are others as well, so the initials are useful to distinguish the writer of A Song of Ice and Fire from the other Georges Martin out there.
Whether it was his own choice to use his initials thus and if so, why; I do not know of a source that answers this.
Community wiki ...
Pen names with initials always look good (arguably better than their fully spelled-out forms), are easy to remember and recognize, and (being shorter) are cheaper to print and easier to throw around in articles and conversation. To cite a few from the top of my head:
Arthur C. Clarke
However, per this interesting ...
There are comments from GRRM about this stating the he does explicitly foreshadow in a way that is extremely subtle and non-obvious to first-time readers.
I don't have the exact source to cite, but I recently watched a video interview where he said something along the lines of: "I like to reward people who re-read my books."
The first time through you ...
There are many hints of Eddard's fate.
As already pointed out, in the first chapter:
Then in Chapter 27 as Eddard discusses the upcoming King's Tourney with the small council, Janos Slynt mentions:
At the end of Chapter 32, Arya asks one of her father's guardsmen
And he responds:
There are other hints in addition to the ones mentioned above, such as ...
I think this specific line is more influenced by Carl Jung.
The brighter the light, the darker the shadow.
One does not become enlightened by imagining figures of light, but by making the darkness conscious.