Wozzeck
The opera is based on a play called  Woyzeck by the German playwright Georg Büchner.  Woyzeck was an unusual drama because, instead of being a story about someone important such as a king or a god, it was about a poor man who is not very smart and is bullied and misused by other people.  When Berg wrote the opera nearly a century later, it was still an unusual story for an opera.  The heroes in operas were usually important people, while working people often had comic parts: they were often servants.  But Wozzeck is a simple man who cannot help what is happening to him.  In drama this is sometimes called an "anti-hero".