The correct answer is Game of Thrones. In fact, not only was the phrase "winter is coming" repeatedly used, "Winter Is Coming" is the first episode of the HBO medieval fantasy television series Game of Thrones. It was written by the show creators David Benioff and D. B. Weiss, in a faithful adaptation of the first chapters of George R. R. Martin's book A Game of Thrones. This episode was directed by Tim Van Patten, redoing the work done by director Thomas McCarthy in an unseen pilot.

The phrase "winter is coming" is the motto of House Stark, one of the Great Houses of Westeros. The meaning behind these words is one of warning and constant vigilance. The Starks, being the lords of the North, strive to always be prepared for the coming of winter, which hits their lands the hardest. The inevitable truth of the words is mentioned by other characters, who occasionally note that sooner or later, the Starks are always right. Be prepared to hear this phrase again and again, it has a deeper, metaphorical meaning. It more generally expresses the sentiment that even if things are good now (summer), always be ready for a dark period (winter) when events often turn bad.

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