One of the distinguishing characteristics of folklore is that it is passed from one person to another in toto, rather than by pointing somebody at a canonical form which can be referenced and which is preserved for all to see. But by this standard, some of the best-known and best-loved "traditional" tales today cannot be called folktales at all. I am referring to the fairy tales most familiar from the Brothers Grimm.
Jakob and Wilhelm Grimm, collectors of the stories in Children's and Household Tales (1812), were but two of many brothers in the Grimm family. They sought to study the German language, culture, and people, and while the phrasing of the stories is entirely their own invention, it is in all cases in a popular form of German and in a lower register of writing intended to match the style of the oral sources from which they collected the tales. Today, while many tellings exist of some of the stories, we tend to regard the versions in Grimm as definitive, at least for many of the tales; in fact, sometimes people point at the bloodier versions in the first edition of the Children's and Household Tales as being the "real" version behind the softer familiar ones.
But make no mistake, the Grimm's writing is not tradition. In many cases the bowdlerizing of the less palatable early versions of the stories was the work of Jakob and Wilhelm themselves, as they were part of one of the first generations of adults to suppose children needed less violent stories and were concerned that their work was being used as a basis for passing the stories on to many more children than ever before. Even the Grimms chose to omit some of the stories seldom found in modern fairy tale collections; by the end of their lives, "Bluebeard" was no longer part of the set. (On the other hand, neither was "Puss in Boots," which is often included in modern abridged compilations and has recently gained greater fame thanks to the Shrek franchise.) Nor should it be supposed that the early versions reflect an authentic, widespread tradition in Germany; a great many of their stories are collected from a single teller, who they identify only as "a peasant woman from the village of Zwehrn near Kassel." This source was, in fact, one Dorothea Viehmann, a middle-class woman of Huguenot descent who was probably heir to many stories of distinctly French provenance; while collected in German, those stories likely do not belong to a pre-Grimm German tradition at all.
Nor is the origin of these tales as obscure as the origin of many pieces of folklore. While the stories had certainly entered an oral tradition by the time the Grimms found them, and some of the specific tales lack known non-folkloric antecedents, the genre of fairy tales as we know them today seem to originate as decidedly authored literary compositions in a genre which enjoyed a brief vogue at the court of Louis XIV of France in the late 17th century. The best-known tales written for this aristocratic audience are those of the Countess d'Aulnoy (many of which appear in Andrew Lang's Fairy Book series) and those of Charles Perrault (who invented the figure of ma Mère l'Oye, or "Mother Goose," to whom he attributed his stories). A number of Perrault stories, often softened a bit, are found in the Grimms' collection. For example, it is Perrault who penned the first known version of "Little Red Riding Hood," while it is the Grimms (or perhaps Frau Viehmann) who introduce us to the ending in which a woodsman comes along and chops open the Big Bad Wolf to rescue Red and her grandmother, miraculously undigested, from the wolf's belly. (This device is almost certainly borrowed from another story, also found in Grimm, in which a mother goat rescues her seven children in the same manner.)
To some degree the literary fairytales of the French court did take their inspiration from an earlier folkloric storytelling tradition, but the specific stories told are either new variants of older tales or entirely new inventions, and the style in which they are written is consciously literary rather than being that of the everyday storytelling that gave rise to their themes. They were also often blatantly moralistic; sometimes, as in the case of most of Perrault's stories, they were followed by an explicit statement of the moral. (This was nothing new - in fact, it was an old device in literary moral tales, which was on its way out by Perrault's day.)
In short, the Grimms came across a woman who knew a wealth of stories that had originated as deliberate literary creations by talented French authors but which had entered an oral tradition, then published the stories she told in their own versions, and theirs quickly became the definitive versions to many people even two full centuries later. Such is the power of a literary canon.