Who is Johann (Jack) von Grimmelshausen from Stories: All-New Tales and what is their importance?

Jack is a young officer in a time period just shortly before the end of the Thirty Years War. He is part of a Hessian patrol who is using a local peasant as a guide in the Spessart region of Germany. He follows the peasant down to the Mummelsee after the peasant tells them stories of how the water changes things that are thrown in. He is faced with a choice of eternal life in the pages of a book, or a return to reality in which he has grown old, and his wife has become fat. Still, he loves her and she loves him, so the choice is relatively simple.