The Confessions by St. Augustine
I'd recommend this translation by Maria Boulding.
Augustine of Hippo's Confessions (and I recommend this translation):
I've read it four times (each time I learn something new) - you have nothing on him: He was attractive, brilliant, had a great career as a rhetorician and hated himself. He wrestled with the question of truth and struggled with chastity. He even pleaded to God "Grant me chastity...but please not yet" (p 149; Book 7, 17). He was 31 when he converted. That being said, he did not do it alone. Saints become saints because they're friends with saints.
The Confessions of Satin Augustine is a good one to give him I think. Here is the Amazon link: