What does a great leader do?

What does a great leader do?  I haven't found a more clear and compelling answer than the one Markus Buckingham gives in his book, The One Thing You Need to Know:

Great leaders rally people to a better future.

The two key words in this definition are “better future.” What defines a leader is his preoccupation with the future. In his head he carries a vivid image of what the future could be, and this image drives him on. This image, rather than, say, goals of outperforming competitors, or being individually productive, or helping others achieve success, is what motivates the leader.

Don’t misunderstand. An effective leader might also be competitive, achievement oriented, and a good coach. But these are not the characteristics that make him a leader. He is a leader if, and only if, he is able to rally others to the better future he sees (The One Thing You Need to Know, pp 59-60.).

(HT: Matt Perman)