Complex sentence: Ernst Keil (6 December 1816--23 March 1878) was a German publisher, bookseller, founder and editor of "Die Gartenlaube", the first successful mass-circulation German language newspaper and a forerunner of all modern magazines.
Split into simpler sentences: Ernst Keil (6 December 1816--23 March 1878) was a German bookseller, editor and publisher. He then launched "Die Gartenlaube", the first successful mass-market German language newspaper and a forerunner of all modern magazines.