Fritz Haber: Hero and Villain or the Two Faces of Science -The industrial process of ammonia synthesis, which began about 100 years ago, has become an essential pillar of life on the planet due to its importance in the production of fertilizers.However, it was also supported the war machine, making it a form of life destruction.Connecting these two realities is an event -World War I -where scientific communities found themselves intertwined in the promotion and development of new weapons, and a leader -Fritz Haber -a scientist-warrior, whose 80 th anniversary of his death is renowned this year.There has never been such a close connection between science and the military, and which were so clearly exposed the two faces of science.In this article we intend to take a trip through the life path of Fritz Haber, a man who was known by important scientific inventions which earned him the Nobel Prize in Chemistry, but also that laid science at the service of the German war machine and further established the foundation of a new form of war, the chemical warfare.