Mathematics needs people to create, to explain, to synthesize, to apply, to teach, to learn, even to proselytize (in socially acceptable ways). If you want fame bordering on immortality, solve a very hard problem or create something that both solves and poses hard problems. If you want instead to be a great contributor to mathematics, do as much of the above as your heart and mind allow.
What would you like to do for mathematics?
Gerhard "Ask Me About System Design" Paseman, 2010.10.27