A truly great musician is a lot of things- not just musical skill. He must have the cult of personality- he must be charismatic, he must be a showman.
To me, the classic exemplification of that is Niccolo Paganini the violinist. He was probably the first musician ever to really have a giant fan following comparable to 'rock stars' today-in that scores of fans followed him, and he toured the entirity of Europe. Furthermore, many people truly thought he had actually made a deal with satan for his gift, and he encouraged it by acting the part of a possessed man not in control on the stage.
His playing was flamboyant, violent- and simply spellbinding. Here was a man who appeared on the quaint music scene with technique that scared ******* richochet bowing, lefthand pizzicato. He once arrived
to perform a sonata in a concert hall, and surprised everyone by playing the entire thing at twelve notes per second.
On another famous occasion, he played a piece so violently that be broke 3 strings and successfully finished the entire thing on the G string- to a wild ovation at it's finish.
He was the original virtuoso- all other individually recognized musicians follow in his footsteps.