Henry Louis Le Chatelier

Henry Louis Le Chatelier was born in Paris on 8 October 1850 and worked through the tail end of the 19th century into the 20th, when chemistry was learning to think in systems rather than just substances. He devised the principle that carries his name: a rule for predicting how a chemical equilibrium responds when conditions change — temperature, pressure, concentration. It became foundational, the kind of idea that gets taught in every intro course because it works. He died on 17 September 1936, decades after the principle had already passed into the common language of the field.