Hashtags are everywhere. They are used by millions across all social media platforms.

But the concept of tagging social media groups or topics with a hashtag is credited to one man, Chris Messina.

He's a product designer who has been working in Silicon Valley for more than a decade.

While running an internet consulting company in 2007, he had an idea.

"There was a small group of us in San Francisco using an early social network called Twitter," Messina said. "We were thinking Twitter needs some kind of group organizing framework."

He got the idea of using a hashtag from Internet chat rooms that had a pound symbol in front of them. He decided to pitch the idea to Twitter, but the company told him it was "nerdy" and that it would never catch on.