Welcome to the Forum
I won't be much help in identifying the greatest anglers, for me and my fly fishing it's a personal commitment. However I will grant that there have been many people who have contributed greatly through their innovation and ability to communicate their skill to the masses. I am grateful that I did not have to think 'all' of this up on my own, I doubt that I could have or would have without those who have went before me.
Anyway, welcome to the forum,