- ~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