I think Barrack Obama has charisma, although I have never met him, but he appeared almost from nowhere and won the US Democratic nomination and the Presidential election just be being himself and people were drawn to follow him in the way the children followed the Pied Piper of Hamelin.
It is this x factor in someone that draws followers, almost against their will, that I would describe as charismatic. Billy Graham was charasmatic, Mother Teresa, The 1st Duke of Wellibgton, in war and in peace. His soldiers said the sight of him on a battle field was worth 10,000 men and in peace, even when he was neither in politics or government, it is clear that in every national crisis people looked to him, including governments for advice and reassurance.
Most of the people mentioned here are high achievers and many have led admirable lives, but charismatic means that someone can be dropped into a desert hundreds of miles from human habitation and by the end of the first day have attracted a small group of people to them who are looking to them them for support and advice and leadership.