The story behind the happiness symbol isn't as cheerful as you'd expect.

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The Mona Lisa might have the most iconic smile in history, but one could argue the yellow smiley face comes pretty close.

What began as an unusual assignment for graphic designer Harvey Ball eventually turned into a world-famous symbol of happiness. In fact, the smiley face can trace its modest origins back to an insurance company in Worcester, Massachusetts in 1963. (Did you know Post-It notes were invented by accident, too?)

After a series of tough transitions, the company’s employees struggled to maintain a cheery workplace. So, the company hired Ball in the hopes that he would design an image to boost morale. (By the way, science has confirmed some pretty convincing reasons to smile more.) In just 10 minutes, Ball drew a simple, smiling face on a yellow background. The price for his genius masterpiece? Only $45.

At first, the company simply printed the face on buttons and posters to give to its employees. But the image quickly gained popularity, and yellow smiley faces started popping up on everything from greeting cards to T-shirts to stickers. Neither Ball nor the insurance company trademarked the soon-to-be iconic design.

“The simple yellow smiley face created in 1963 (probably) has led to tens of thousands of variations and has appeared on everything from pillows and posters to perfume and pop art,” according to the Smithsonian. “Its meaning has changed with social and cultural values: from the optimistic message of a 1960s insurance company, to commercialized logo, to an ironic fashion statement, to a symbol of rave culture imprinted on ecstasy pills, to a wordless expression of emotions in text messages.”

Over time, many legal battles ensued over who could truly claim ownership over the legendary design. (At one point, even Walmart got involved!) But it’s still widely accepted that Ball was the first to invent the iconic yellow smiley face.

Regardless of its origins, one thing is clear. While initially intended to cheer up a small company in Massachusetts, the smiley face’s positive message now reaches across the world.

Think that was interesting? Check out some of the craziest invention stories ever.

Sources: Smithsonian, Mental Floss