Using it as a defensive measure against the French

The English leadership is well known to have used the specter of “Vikings” to keep others at bay. One of the best known uses of these tales is to limit the invading Normans to the southern part of England where a more central defense could be set up against.
The Normans fully believed in the mythical vikings, and even created a set of prayers that were said to ward off “demons” conjured by Norse Gothi. Most of these were considered heresy by the church and quietly banned, but were still used in private for several centuries. Markings of them have been found in the margins of old manuscripts from the late 12th century in Calais.
The Normans told children tales of ice breathing dragons that would sweep in and slowly consume the world if they were not strong enough to fight the English. This was later adopted by George R. R. Martin for his “Game of Thrones” series.