In a nutshell: This man was a largely self taught mathematician. Much of his work did cover previously established ground, but he rediscovered and studied hundreds of years of progressive Mathematics without direction. Sort of a David and Goliath story really. Genius often comes from the places you least expect it.

It is also rumored that Ramanujan credited his mathematical abilities to the deity he worshipped (sorry I can't recall which one at the current time). He said that the deity actually visited him in his dreams.