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.
"I was a little bit dejected but I laughed," he said. "I thought, I just don't know how else we're gonna solve this problem."
He didn't give up. Instead, he strated asking friends to give the hashtag a try.
In October of 2007, one of his friends was tweeting about a San Diego wildfire. Chris asked him to add #sandiegofire to his tweets. It didn't take long for others to start using the same hashtag.
"The fact that other people actually emulated him in real time during those fires gave me a sense that this could actually work," Messina said. "It turned out that lots of people wanted to have their voices heard and participate in a global conversation."
The idea caught on, and in 2009 Twitter added an option for users to search for hashtags.
When Instagram launched in 2010, users started tagging photos with hashtags like #nofilter or #yolo. Facebook adopted them in 2013.
While some users simply want to brag on social media, others are using the versatile tool for change. It's what some media outlets are calling "hashtag activism." #NeverAgain, #MeToo and #BlackLivesMatter movements have gained incredible momentum thanks to their hashtags.
The hashtag even had incredible influence on the 2016 U.S. presidential election with tags like #imwithher, #MakeAmericaGreatAgain, #lockherup and #feelthebern.
And even though there are now countless hashtags, Messina never made a dime off of the idea.
"I didn't create this idea for Twitter," he said. "I created this idea for the Internet and I wanted anybody who could write text on the Internet to be able to participate in global conversations."