As with all things we need to start at a true beginning, as opposed to the point we normally launch into things at, based on our own capabilities, experience and knowledge-so-far.
As the question is "What MAKES a great leader"? meaning what comes before or leads up too, not after the fact attributes.
A great leader is a great listener, absorber, observer, continual learner. In turn and attempting balance, they provide feedback with conviction and in a to-educate mode.
A difference between the proven leader and the great leader is the latter rarely plateau's with their 'input' or connection process; while the proven leader may not be employing ideas and approaches that continue to be as impactful and fully-applicable to current and near-future needs.
This, I believe is the difference between leaders like Warren Buffet, Bill Gates, Sir Richard Branson, Bono (to name some familiar) and the recent Executive manager asked to step-down or a constituency patiently(?) awaits leader's end-of-term.