What I am getting at is that the best in most fields have it in them. That does not strive to learn all they can about the technical details of their craft, but that isn't what makes them great.
'Greatness' is an entirely subjective concept that has little to do with actual competence and everything to do with salesmanship. Competence may help with this, but is hardly the only way.
For instance, Giorgio Armani is a mediocre designer but an excellent salesman, who has built up 'greatness' around his own name. Kim Il Sung/Jong Il/Il Sun are renowned as 'great' in their own country (largely through propaganda, which is a form of salesmanship), but that also has little to do with competence.
If you want to justify someone's 'greatness' to a sceptical audience, don't namedrop - that doesn't impress anyone who's not already in the loop and part of the 'in-group'. List their achievements.