There are currently five books in the "A Song of Ice and Fire" series with a few more in the works. However, author George R.R. Martin's original plan was for the series to be a trilogy.
In 1993, sci-fi/horror novelist and former Hollywood screenwriter George Raymond Richard Martin wrote a letter to his publisher Harper Collins outlining his plans for an epic series titled A Song Of Ice and Fire. UK book retailer Waterstones posted pictures of the letter on their Twitter in February 2015 then deleted it a day later, but not before eager watchers on the wall got a hold of it.
His letter, which gave a brief synopsis of the trilogy’s story arc and a more detailed synopsis of the first book A Game of Thrones is pretty similar to what the series became at its core. But GRRM made a few major changes between the time he wrote this letter and the time he wrote A Game Of Thrones that lead the readers to wonder what could have been in another universe. Notably:
ASOIAF was intended to be a relatively concise trilogy rather than a sprawling heptalogy
GRRM originally intended the Dothraki invasion to work out, and planned for Dany to try to reach Westeros much sooner
The story was set to span over a longer period of time that would take Bran, Arya, Jon, and Dany from childhood to adulthood
A love triangle between Jon, Arya, and Tyrion was originally planned
Robb is killed in battle and Catelyn is killed by the Others (White Walkers)
However, at their core, much remains the same. The 5 characters GRRM planned to center the story on – Jon, Dany, Arya, Bran, and Tyrion – are all integral to the series, and “the suspense always ratchets up a notch when you know that any character can die at any time” is a feeling that any fan of this universe knows too well.