Euclid

Euclid taught mathematics at Alexandria during the reign of Ptolemy I Soter (323–283 BC). This is virtually all that is known about his life. Even this much may be unreliable — the ancient biographical tradition is thin and often confused him with the philosopher Euclid of Megara, who lived a century earlier.

The Elements (Stoicheia) is the most successful textbook ever written. In thirteen books, it builds the foundations of geometry and number theory from a small set of definitions, postulates, and common notions, proceeding by rigorous logical deduction to increasingly complex results. The method — axiomatic, deductive, cumulative — became the model for mathematical reasoning for over two thousand years. Abraham Lincoln taught himself logical thinking from Euclid. Newton cast the Principia in Euclidean form.

The Elements was not entirely original — Euclid synthesised and reorganised the work of earlier mathematicians, including Theaetetus and Eudoxus. His genius was in the organisation: the careful selection of axioms, the logical ordering of propositions, and the relentless clarity of the proofs. The work has been continuously in print since 1482 and has been translated into more languages than any book except the Bible.