One highly fanciful legend exists about the origin of the first gargoyle. I have come across it in several different books, so I figured I would share with you.
“La Gargouille, a dragon [who] was said to have regularly terrorized the French town of Rouen. On its annual visits, the dragon demanded of the townspeople a virgin maiden, although more often than not, he was given a convicted criminal instead. As the story goes, the villagers grew tired of La Gargouille’s demands. A priest arrived upon the scene and promised to subdue the dragon if, in return, the townspeople would build and join his church. Doubting his chances for success, they readily agreed and the priest set off to confront the dragon.
Shortly after leaving town, the priest came upon La Gargouille. Using the sign of the cross and other Christian powers, he quickly subdued the beast, then led the docile dragon on a leash back to Rouen. Wanting to ensure their permanent freedom from their oppressor, the townspeople burned La Gargouille at the stake. The beast’s head and neck did not burn, however, undoubtedly due to its lifelong habit of breathing fire, which had toughened its skin. The townspeople mounted these charred remains on their newly constructed church as a symbol of victory over evil. This story was set in stone when a dragon was carved on the exterior of the cathedral at Rouen, where it can be seen to this day.” (Trew Crist, Darlene. American Gargoyles: Spirits in Stone. New York: Clarkson Potter/Publishers, 2001. p15.)
It is obvious that this tale, charming though it may be, is not really true. However, many stories have a basis in fact, and this may be no exception. It has commonly been proposed that the creatures depicted by gargoyles are holdovers from the pagan religions that predated Christianity in western Europe and were placed on the outsides of churches to make new converts more comfortable. Therefore, it may actually be true that gargoyles played a role in conversion, though unlikely quite to the magnitude suggested in the legend.