In German, von is a preposition which approximately means 'of' or 'from'.
When it is used as a part of a German family name, it can indicate a member of the nobility, like the French, and Portuguese "de". At certain times and places, it has been illegal for anyone who was not a member of the nobility to use von before their family name. However, in the Middle Ages the "von" particle was still a common part of names and was widely used also by commoners.
See also van
"Hans von Duisburg" meant Hans from (the city of) Duisburg.