There are many qualities of leadership successful leaders have, but the most critical differentiator is the capability to inspire.  According to Jack Zenger and Joseph Folkman writing  for the Harvard Business Review, their study on 360 degree feedback from nearly   50,000 leaders globally showed this quality as the most important.

I have found this true in my personal experience.  None of the best were effusive extroverts or rah-rah types, although all were quietly compelling in his or her own way.  The capability to encourage and coax the best out of people, and have them give it willingly and without restraint, is truly a gift.