is it adapted from any novel?
Yes from the novel of the same name
Game of Thrones
Game of Thrones is an American fantasy drama television series created by David Benioff and D. B. Weiss for HBO. It is an adaptation of "A Song of Ice and Fire", George R. R. Martin's series of fantasy novels, the first of which is "A Game of Thrones" (1996). The show was both produced and filmed in Belfast and elsewhere in the United Kingdom. Filming locations also included Canada, Croatia, Iceland, Malta, Morocco, and Spain. The series premiered on HBO in the United States on April 17, 2011, and concluded on May 19, 2019, with 73 episodes broadcast over eight seasons. 
when did filming for game of thrones start July 26, 201 who are the main characters in this series? Lord Eddard "Ned" Stark, Catelyn  and Robb to name a few
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Game of Thrones [SEP] Introduction
"Game of Thrones" attracted a record viewership on HBO and has a broad, active, and international fan base. Critics praised the series for its acting, complex characters, story, scope, and production values, although its frequent use of nudity and violence (including sexual violence) was criticized. The final season, especially its last four episodes, received significant criticism for its condensed story and creative decisions, with many considering it a disappointing conclusion. The series received 59 Primetime Emmy Awards, the most by a drama series, including Outstanding Drama Series in 2015, 2016, 2018, and 2019. Its other awards and nominations include three Hugo Awards for Best Dramatic Presentation, a Peabody Award, and five nominations for the Golden Globe Award for Best Television Series – Drama.