Heisenberg

Werner Heisenberg — German theoretical physicist who developed quantum mechanics and formulated the uncertainty principle (1927) — demonstrating that the position and momentum of a particle cannot both be precisely measured simultaneously — one of the foundational discoveries of 20th century physics.

Discovered that the observer always disturbs the observed — the uncertainty principle showed that there is an irreducible limit to measurement precision baked into the fabric of reality (not just an engineering limitation) — demolishing the classical assumption that nature is in principle fully knowable and measurable.