"The Smurfs" is a cartoon serial which is very popular in Europe (particularly in France and Germany, I should think). It basically revolves around a band of 99 or 100 or 101 (varies from show to show) little blue guys who run into problems all the time. Every single smurf represents a different character (i.e. there is a joke smurf who gives everyone explosive presents, a smurf who hates everything around him, a female smurf, a cook etc.). Their adversary are an evil wizard and his cat (Gargamel and Azrael). In the earlier shows, Gargamel was after the smurfs because he wanted to turn them into gold, while in the later seasons, he wanted to eat them. More characters were introduced as time advanced, and the show turned bad with them.
Needless to say, "The Smurfs" were a childrens serial, so their problems were basically social or of other harmless sort (for example failed bridge building).
There was and is lots of smurf merchandising, comic books, real books, figures (these are the most popular, and virtually everyone in Germany has at least one of them) and more.