To see WHY he is so famous just look at his work, His paintings speak for themselves:
http://www.google.com/images?client=safa…
HOW he got so famous is that he traveled the world studing and doing roughly 900 oil paintings and more than 2,000 watercolors, as well as countless sketches and charcoal drawings.
Active marketing is usually another factor in achieving fame.
Historically in a time when the art world focused, in turn, on Impressionism, Fauvism, and Cubism, Sargent practiced his own form of Realism setting him apart.
http://en.wikipedia.org/wiki/John_Singer…
