As a child, Gerhard Lang's mother had made him a basic advent calendar so
that he could count down the days until Christmas. She placed 24 sweets onto
a piece of cardboard and each day the young Gerhard would take and eat a
sweet. When he grew up Gerhard Lang made the first printed advent calendar
in 1908.
Later, in 1946, we see Richard Sellmer producing calendars in
Germany. The US authorities had to grant him a license in the now post war
Germany which led to his advent calendars becoming known and indeed very
popular in the USA.