It's a little strange to think of the social media hashtag being "invented." Suddenly they just seemed to start popping up on Twitter and Instagram, and soon we were all using them. But in fact, the hashtag was created on this day 10 years ago, the 23rd of August 2007, by a Google and Uber engineer called Chris Messina. You can see his original hashtag tweet below.
Messina's idea caught on so spectacularly that it's now estimated that 125 million hashtags are used on Twitter every day.
"I feel a great deal of gratitude and honour to have contributed such a fundamental aspect of social media," Messina told The Australian in an interview to mark the hashtag's birthday. "It’s thrilling to see how this little idea that came out of a very specific moment in the evolution of the Internet took off and has grown into something far bigger than me, bigger than Twitter or Instagram, and that will hopefully maintain its relevance for a long time to come."
To mark the 10th birthday of Messina's creation, several outlets including the BBC have compiled lists of the most popular hashtags of all time. There's no totally definitive ranking, but political hashtags like #BlackLivesMatter, #Brexit, and #EdBallsDay all figure prominently in any round-up of iconic Twitter hashtags.
Other hashtags that went super-viral include #HeForShe, which exploded after Emma Watson gave a 2o14 UN talk encouraging men to do more to support women's rights, and #TheDress, which many of us used last year to share our verdicts on whether that dress was really black and blue, or white and gold. When the ALS Ice Bucket Challenge became a social media phenomenon in 2014, the #IceBucketChallenge hashtag duly went viral, too.
Entertainment-based hashtags including #GBBO, #GoT, and #StarWars are also right up there, of course. And let's not forget that perennial favourite, #FollowFriday.