Answered by Susan, Hiring Expert at Praxair, Inc., on Monday, June 3, 2013
Sometimes questions like these are used, because there is no right or wrong answer, but rather the Company wants to understand more about your personality, what makes you "tick", what drives your motivation, etc.
So think about the answer in terms of a company evaluating you as a potential employee to invest in. Your answer could be a) "I want to be known as a great leader of people, helping them do things they never thought they could do", or b) "I want to be the scientist who discovered the cure for cancer", etc. Give them some insight into what you are passionate about (but put this into business oriented terms).