Traditionally on December 5th and 6th, St. Nicholas walks from house to house in the cities and villages of the Alps to admonish and laud young and old. He is mostly accompanied by a Krampus (an evil creature, a devil of sorts), who is going to punish the bad children and adults on St. Nicholas′ command. For the honest children he normally has little presents.
St. Nicholas himself is a Christian figure, more precisely the former bishop of Myra. As son of a well situated family he started to help poor people who lived in deep poverty. He was supposed to have miraculous vigor and so he became patron of the seamen, children and poor people. (See a previous post about St. Nicholas and his care for the poor here.) In most modern versions of the St. Nicholas story, he is accompanied by a monster or servant (the Dutch describe his assistant as Black Peter) who punishes the bad children while Nicholas himself rewards the well-behaved children.
The figure of the Krampus is based on pre-Christian custom. The Krampusse not only punish the bad children but had the function at one time of driving out the winter devils and blizzard sprites. Originally the custom of the Krampus was spread over all of Austria but was forbidden by the Catholic Church during the Inquisition. It was prohibited by death to masquerade as a devil or an evil creature and so this custom only survived in some remote, inaccessible, regions of the Alps from where it slowly spread back across the western parts of Austria again. Today the Krampusse revels are especially popular in Salzburg.