Lisp
One of the world's oldest programming languages — John McCarthy, MIT, 1958. Famous for its parentheses and for code = data (homoiconic).
The family includes Common Lisp, Scheme, Clojure, Emacs Lisp, Racket. Pioneered: garbage collection, dynamic typing, first-class functions, REPL, macros that transform AST. Influenced every later language. "Lisp is the most intelligent way to misuse a computer" (Edsger Dijkstra). Short for "LISt Processor".