The dragon is a late arrival. The earliest material about George, in Greek and Latin and in Syriac, Coptic and Ethiopic versions, is martyrdom literature: a soldier who refuses to sacrifice and is tortured through an escalating and frankly extravagant sequence, killed and revived more than once, before finally being beheaded. That material was already circulating widely by the fifth century, and George was venerated across the Christian East long before anyone attached a reptile to him. A decree associated with the late fifth century listed his acts among writings to be read with caution precisely because of their extravagance, which is evidence of how popular they had become.
The dragon episode appears in the Latin West only in the eleventh and twelfth centuries, in the period of the crusades, and its wide circulation is owed above all to the Golden Legend, the compilation of saints' lives made by the Dominican Jacobus de Voragine in the thirteenth century, which was among the most copied books of the later Middle Ages. From there the scene passed into altarpieces, civic pageantry, guild processions and heraldry, and George was adopted as patron by soldiers, by military orders and eventually by whole countries, including England, Georgia, Ethiopia and Catalonia, and by cities from Moscow to Genoa. The rescue of the princess, which occupies a few lines in the legend and is not its stated point, became in art the whole of the story.