Edsger Dijkstra

Edsger Dijkstra (1930–2002) was a Dutch computer scientist with strong opinions and beautiful handwriting — he wrote hundreds of essays by fountain pen and numbered them "EWD". He helped turn programming from a bag of tricks into a real science, and along the way invented one of the most-used algorithms on Earth.

The stroke of genius

If your phone has ever found you the fastest route home, thank Dijkstra. His shortest-path algorithm — which he famously dreamed up in about twenty minutes while sipping coffee with his wife — is the backbone of route-finding, and its clever cousin A* search powers game AI and maps today. He also gave us the semaphore for coordinating programs and helped kill the tangled "goto" statement.

Dijkstra was gloriously blunt. He argued that testing can only ever prove your code has a bug, never that it doesn't — you need proof for that. He once wrote that asking whether a computer can think was "about as interesting as whether a submarine can swim," and he graded exams on a scale where the top mark meant "I couldn't have done better myself." Colleagues both loved and dreaded landing in his inbox.