The origin of the term is quite interesting. From the wiki link:
The term robber baron derives from the medieval German lords who charged nominally illegal tolls (tolls unauthorized by the Holy Roman Emperor) on the primitive roads crossing their lands or the larger tolls on ships traversing the Rhine—all such actions without adding anything of value,(see robber baron) but instead lining one's pockets to the detriment (added costs) of the common good.
The term robber baron derives from the medieval German lords who charged nominally illegal tolls (tolls unauthorized by the Holy Roman Emperor) on the primitive roads crossing their lands or the larger tolls on ships traversing the Rhine—all such actions without adding anything of value,(see robber baron) but instead lining one's pockets to the detriment (added costs) of the common good.