The brothers Jacob (1785–1863) and Wilhelm Grimm (1786–1859) were German cultural researchers and authors who collected and published German folklore during the 19th century.
Other than sometimes falsely assumed, the brothers didn't make up the fairy tales themselves, but penned down popular German folk tales. With the movement of Romanticism that started in the late 18th century, the interest in fairy tales revived. While Germany was still an assembly of kingdoms and (grand) duchies, the brothers strongly believed that national unity relied on the knowledge of the common cultural past that was reflected in folklore.
In the introduction to their first book of collected fairy tales, the Grimms explain that they had travelled through Germany to talk with storytellers who supplied them with tales. Since the stories had been handed oraly from generation to generation, they often heard various versions of tales that were in fact the same stories. In these cases, the Grimms picked out the common content and molded it into a single tale.
The first edition of Children's and Household Tales ("Kinder- und Hausmärchen") was published in 1812, but was in a constant state of alteration. During their lifetime, the work was published 17 times. Wilhelm was the main editor of the two, making the tales stilistically similar, adding psychological and sometimes religious plots and dialogue.
Although the editions that are now common are still quite grim - quite some (children's) heads roll, people are cooked more than once, et cetera -, the very first edition of Children's and Household Tales was even more cruel. An example of such an alteration would, however, only be that it was not Snow White's real mother that would try to kill her out of jealousy, but her step mother.
Though fairy tales such as Snow White, Cinderella and Hansel and Gretel are mostly read to children nowadays, most of the tales the Grimm's collected were not originally intended to be children's tales. Nevertheless, the introduction to the 1819 edition, the Grimms explain they "carefully omitted every expression that could be unsuitable for children". Adaptions by, for example, Walt Disney, paint a distorted picture of the original versions. For example, in The Frog Prince, the princess doesn't kiss the frog at all - but throws him against the wall. Cinderella's step sisters cut off parts of their feet in order to fit in the golden (not glass!) slipper, and when their fraud is revealed, Cinderella's doves strike the evil step sister's eyes, leaving them blind for the rest of their lives. Snow White's evil step mother had to dance in burning red shoes until she dropped down dead.
Less well known today is the German dictionary the brothers started working on in 1838. Their goal was to give an explanation, history and analysis of each word in German language. In 1852, they published the first volumes of the dictionary, but they weren't able to finish it during their lifetime. Still, 32 volumes were published until 1960. The dictionary can be viewed online on a special website of the Trier University.