The book which changed their life:
1. GH Hardy: by Carmille Jordan’s Cours d’Analyse:
“I shall never forget the astonishment with which I read the remarkable work … and I learnt for the first time as I read it what mathematics really meant.”

2. Ramanujan : George Carr’s
“A Synopsis of Elementary Results in Pure & Applied Mathematics”
(4,400 results without proofs)

3. Riemann : Legendre’s book

4. Hardy/Littlewood:
Landau 2-volume “Handbuch der Lehre von Der Verteilung der Primzahlen”
(Handbook of the Theory of the Distribution of Prime Numbers)

5. Atle Selverg (Norway): Ramanujan’s “Collected Papers”

Note: This blogger’s mathematics ‘fire’ is rekindled by John Derbyshire’s “Unknown Quantity”.