~300 BCE, Greek mathematician active in Alexandria
Elements: thirteen books systematizing geometry, number theory, and mathematical logic from five axioms and five postulates
established the axiomatic method: start from self-evident truths, derive all results through rigorous logical proof
Euclidean algorithm: efficient procedure for computing greatest common divisor, still fundamental in computer science and cryptography
proof of the infinitude of primes: one of the earliest and most elegant proofs in mathematics
parallel postulate (fifth postulate): its eventual questioning led to non-Euclidean geometries (Gauss, Lobachevsky, Riemann)
Elements remained the standard mathematics textbook for over two thousand years
foundation of mathematical rigor that underpins all formal systems including proof verification in distributed protocols