An idea was born that transformed the entire photo industry like few ideas before that or since. His first prototype was completed in 1913. Leitz was unsure about the marketability of the new design. Leitz had already experienced a disaster in marketing cameras, introducing two models of folding plate cameras just after the turn of the century, both of which sold dismally. In spite of that, and advice not to market such a camera, in 1925 the camera went into production, and became available for sale.
Gradually the camera was improved. Interchangeable lenses were added, as was a coupled rangefinder, and slow shutter speeds.
In 1932, Zeiss challenged Leitz with the introduction of the Contax. Through World War II these cameras were the two professional 35mm rangefinder systems, and the competition was intense. After the end of the war, all German patents were made available to the public as part of the war restitution. This actually allowed the Japanese camera industry to flourish, and one of the most copied designs was the Leica (the Contax was too difficult to build).
Through the fifties and sixties, Leitz, and the rest of the German camera industry continued to lose market share. When other manufactures abandon producing professional grade rangefinder cameras, Leica inherited that entire market, and they have basically been a specialty manufacture ever since. They did market (and still do) an SLR line, as well as high end point-and-shoot cameras. But neither of these lines holds much market share.
Throughout this whole time cameras have been a sideline product for Leitz. Their primary products have always been optical; microscopes, binoculars and other optical goods.
For help identifying a Leica camera, check out Leica Identification