The MUSH is based (with the author’s permission) on the A Song of Ice and Fire series by George R.R. Martin. The series consists of A Game of Thrones, A Clash of Kings, A Storm of Swords, A Feast for Crows and A Dance with Dragons. At this point, two more books called The Winds of Winter and A Dream of Spring are planned. GRRM has also written three novellas in this setting, called "The Hedge Knight", "The Sworn Sword" and "The Mystery Knight" as well as two books of “fake history”; The World of Ice and Fire (co-authored with Elio M. García and Linda Antonsson) and Fire and Blood.
A Song of Ice and Fire is a gritty, medieval-inspired fantasy set in the world of Westeros. It is a world of strange seasons—summers that last for years and winters that can last a lifetime—as well as of both chivalrous knights and ruthless politics. Magic was once common, and the Targaryen kings possessed dragons that could wreak havoc to their enemies, but now magic has faded and the dragons have all died. Though the game is not set at the time of the books, but rather some 140 years prior to them, most of this holds true for this time period too. The main difference is that House Targaryen still rules the Seven Kingdoms and that, as a result of this, the political situation is less chaotic, less ruthless and less dangerous than in the books. However, the game of thrones is still very much a high-stakes game.
When the game opened the IC year was 158 after Aegon’s Landing (Aegon the Conqueror was the first Targaryen king and the one who established the Seven Kingdoms) and King Daeron I—called the Young Dragon—had just conquered Dorne and made this previously independent realm a part of the Seven Kingdoms. Our aim is to stay as canon as possible, both in terms of theme and in terms of storyline. This means that since the opening King Daeron I has died in Dorne (as the Dornish rebelled and became independent once again) and been succeed by his brother, King Baelor. It also means that House Targaryen cannot be overthrown by, for example, House Lannister. But there is a lot we do not know about this period, so the fates of most individuals is not pre-determined.
The Game of Thrones TV show is considered non-canonical for the purpose of the MUSH wherever it deviates from A Song of Ice and Fire.