The Slinky was invented in 1943 by Richard James, a naval engineer, who was attempting to develop a new tension spring for use in naval ships. However, when he accidentally dropped one of his prototypes and watched it 'walk' down a series of steps, he realized its potential as a toy. The first Slinky was sold in 1945, and it quickly became a popular household item, leading to millions of sales and a place in American pop culture.