Alonzo Church (1903–1995) was an American mathematician and logician who asked one of the deepest questions in all of computing: what does it even mean for something to be "computable"? His answer helped launch computer science before computers really existed — and one of his students went on to become very famous indeed.
Church invented the lambda calculus, a tiny, elegant system where everything is a function
— the ancestor of every functional programming language. Working at the same time as his
student
Church was famously meticulous. His lecture notes were so precise that students said they could be sent straight to the printer. He wrote in a careful, coloured-ink style, kept his papers in fireproof order, and reportedly worried about being struck by lightning. He taught for decades and, as founding editor of a major logic journal, shaped the field for generations — a quiet giant standing just behind the more famous names.