In 1953, a fledgling company called Rocket Chemical Company and its staff of three set out to create a line of rust-prevention solvents and degreasers for use in the aerospace industry, in a small lab in San Diego, California.
It took them 40 attempts to get the water displacing formula worked out. But they must have been really good, because the original secret formula for WD-40—which stands for Water Displacement perfected on the 40th try—is still in use today.
More info... The owner of that company took a can of it home (it wasn't aerosol at the time). His wife was the one that discovered all the OTHER uses for WD-40. Uses such as wood polish, degreaser, squeaky wheel fixer, etc. They only intended it as a corrosion preventative.