John McCarthy
Created Lisp and the idea that code is data; coined the term "artificial intelligence."
John McCarthy was an American computer scientist who coined the term "artificial intelligence" and, in 1958, created Lisp — the second-oldest high-level language still in use. Lisp introduced ideas that took the rest of the field decades to absorb: recursion as an everyday tool, garbage collection, the conditional expression, and above all the principle that code is just data.
Because a Lisp program is itself a Lisp data structure, the language can read, transform, and generate its own code — and can even be defined in itself, as McCarthy showed with the famous metacircular evaluator. The essay Lisp and code as data traces why this still matters. He belongs to languages & paradigms.