[elliptic]

I don't think those 3 are any less well-known than other physicists and mathematicians of similar accomplishments. Ramanujan, in particular, because of his romantic story, is far more well known than his influence might suggest. His intellect might well have been the equal of Riemann's, but one can't honestly say his contributions even approach Riemann's. The same goes for the the physicists - Bohr was one of the three or four most important physicists of the last century, and Heisenberg was one of the top 10, probably.