A mathematician's apology (PDF). The early chapters are mostly grumbling about getting old. But then he starts talking about mathematics, with real poetry and love for the subject. Very nice.
Eudoxus. This ancient Greek anticipated Dedekind cuts and calculus. He also mapped the heavens and the earth. Yet no work of his survives--only frequent citations in the works of Euclid, Aristotle, Hipparchus, and more.