On June 7, 1952, Grace Hopper demonstrated the first working compiler — a program that translates human-readable instructions into machine code — to her colleagues at the Eckert-Mauchly Computer Corporation.

Before Hopper, programming meant writing in machine language: long strings of binary that spoke directly to the hardware. Every program required intimate knowledge of the specific machine it ran on. Hopper believed there was no reason for this.

She wrote the A-0 compiler. When she showed it to her colleagues, several told her it was impossible — that a computer could not write its own programs. She later said that "the most dangerous phrase in the language is: we've always done it this way."

A-0 led directly to FLOW-MATIC, the first programming language to use English-like words, which led directly to COBOL — the language that still runs the majority of the world's banking and insurance systems today.

Hopper served in the U.S. Naval Reserve, rising to Rear Admiral. She was the oldest active-duty commissioned officer in the U.S. military when she retired in 1986 at age 79. She received the Presidential Medal of Freedom posthumously in 2016.

When asked why she kept a clock on her wall that ran backwards, she said it was to remind people that the way things are isn't the only way things can be.