The recent discovery of an archive full of personal documents of the philosopher and biologist Ludwig von Bertalanffy, founder of the General System Theory, paved the way for a reconsideration of important elements concerning his life and thought. This updated biography of a thinker, who is equally often cited as misjudged, takes into consideration all of his publications, his correspondence, as well as the secondary sources devoted to him, and attempts to reveal his richness and complexity to a general reader. This biography thus aims at initiating and promoting a study that is both critical and appreciative of his oeuvre. It equally seeks to navigate between two all too common pitfalls found in connection with von Bertalanffy: hagiographic temptation and reductive judgements, which are often ideologically motivated.