Krampus is an anthropomorphic horned figure from Alpine folklore, who during the Christmas season scares children who have misbehaved, assisting St. Nicholas (the first of three good December figures; the other two being Santa Claus and Ded Moroz).
The pair visit children on the night of the 5th December, and St. Nicholas rewards the well-behaved children with modest gifts such as oranges, dried fruit, walnuts and chocolate whilst the badly behaved ones only receive punishment with birch rods and lumps of coal by Krampus.
Krampus's role as a helper of St. Nicholas extends to where he is sometimes known as the "Shadow of St. Nicholas," ergo making him a type of "Christmas boogeyman."