Does leadership improve societies?

Leadership is a powerful tool capable of improving society in a great measure, but it can regress one too. It all depends on leader and his/her aspirations. Throughout history there are various examples how people whose intentions are honest can bring a lot of good in society and change people's lives for better not years, but decades in the future. Some of them are Mahatma Gandhi, Martin Luther King, Jr., Nelson Mandela etc. On the other side we can mention Osama bin Laden, one of the people whose leadership is associated with destruction and ill-intented aspirations. In general, I believe that leadership does improve societies, but it is potential atribute for bad thing as well.