In Geoffrey of Monmouth's Historia Regum Britanniae, Merlin delivers a prophecy of seven kings who would rule Britain, a vision that was later interpreted as foretelling the line of English monarchs. This prophecy was used by the Plantagenet kings to legitimize their rule, particularly Edward I, who saw himself as fulfilling Merlin's vision. It became a cornerstone of English royal propaganda and national identity.

The prophecy of the seven kings became a recurring theme in English literature, from the chronicles of the Middle Ages to Shakespeare's history plays. It provided a mythological framework for understanding English history and was used by poets and playwrights to comment on contemporary politics, blending prophecy with national myth.