That little λ you type every day?
It began as a typesetting workaround. Alonzo Church (1903–1995), a reserved Princeton logician, wanted a clean way to write functions.
He borrowed the “hat” notation (ˆx) Whitehead and Russell used in Principia Mathematica for classes, moved the caret in front to distinguish functions, then changed it to λ because printers handled it better.
Years later he joked the choice was almost “eeny, meeny, miny, moe.” That humble Greek letter became the foundation of functional programming and the Church-Turing thesis that still defines what computers can do.