A labyrinthine riddle has plagued mankind for generations: What walks down stairs, alone or in pairs, and makes a slinkity sound?

At long last, the answer came in the form of a simple-yet-fun children's toy known as the Slinky. At an estimated 300 million sales and counting, the Slinky has been a childhood staple for over 60 years.

But how did something as innocuous as an industrial-sized metal coil emerge as a product that could be "fun for a girl and a boy?"

By accident, of course.

Slinky inventor Richard James was a US Naval engineer. In 1943, while stationed at the Cramp shipyards in Philadelphia, James was working on a horsepower detection meter for naval battleships. A large torsion spring involved in the design fell from his worktable and toppled to the ground in the classic, end-over-end, slinkity manner. James shrewdly told Betty, his wife and future business partner: "I think I can make a toy out of this."

The couple spent the next 2 years perfecting the product. James took out a $500 loan to build machinery to construct the coils en masse. Since the toy is relatively cheap to produce, James was able to make 400 units for initial sale. It was Betty who dubbed the toy "Slinky" - named after a Swedish word meaning sleek or sinuous.

In 1945, the Slinky was unveiled at Gimbel's Department Store in Philadelphia, just in time for the Christmas season. James asked the store to set up an inclined plane in order to demonstrate the Slinky's acrobatic abilities for curious customers. Petrified that nobody would be interested, he even asked a friend to pretend to enthusiastically buy one.

But it wasn't necessary: All 400 units sold out within 90 minutes. Richard and Betty had stumbled onto a goldmine.

Under the brand James Spring & Wire Company, the Jameses began production in Philadelphia, later to relocate to Holidaysburg, Pennsylvania. The Slinky's basic design underwent only 2 changes from its initial release: The Swedish blue and black-colored steel was switched to American-made silver metal, and the ends were crimped as a safety precaution.

As the toy grew in popularity, the company debuted variations on the concept. Soon, toy shelves were filled with plastic Slinkys, Slinky Jr., Slinky Dog, Slinky Eyes and multicolored Slinky. The classic Slinky jingle, featured in the famous 1963 commercial, only added to the toy’s iconic appeal.

Staying true to its engineering origins, the Slinky coil has been used in a number of innovative ways. During the Vietnam War, soldiers discovered that the toy strengthened radio reception when attached to antennae and draped over a tree branch. By moving and twisting the ends of a Slinky, physics professors are able to demonstrate wave motion, acoustics and seismology.

Following a 2003 merger, Slinky is now a product of Poof-Slinky, Inc.