robert-kanigel's book, "the man who knew infinity" is an excellent chronicle into his life, and cambridge's culture during 20th century. it was hardy who created a rising scale of mathematical abilities as follows:

  g.h.hardy - 25
  littlewood - 30
  hilbert - 80
  ramanujan - 100

hardy once described the formulas in ramanujan's first letters as "these must be true, if they are not, nobody would have the audacity to invent it."