The slinky was invented by American naval engineer Richard T. James in 1943, when he was searching for a way to suspend instruments in ships at sea. He realized that with the right kind of spring steel, the slinky would be able to walk, even down a flight of steps. It can also do various tricks and move in ways people aren't used to, such as this comedy routine by Dr. Vinkelstein, where he walks it off his hat, and gets a jumbo slinky going with cool color shifts.

The toy didn't sell a single unit when first displayed, because no one knew what it even was. But after people saw it demonstrated walking on its own down an inclined board, it took off, and has sold over 300M units as of 2005.

The inventor seemed to go off the rails in the late '50s, and began giving large amounts of the company's money to a religious sect in Boliva. His wife Betty James divorced him, and ran the company herself until 1998.

Original slinky:

There were various knock-on toys from the same company, such as slinky dogs, or this set of crazy eyes.