Twitter co-founder Jack Dorsey blasted out more than 50 short videos from Ferguson, Missouri, in August 2014 as tension mounted over the police shooting of an unarmed black man.
Over the course of a week, Dorsey, who grew up in neighboring St. Louis, shared scenes of protesters marching, dancing and holding signs. His tweets bore the hashtag #BlackLivesMatter, helping to push the burgeoning movement into the mainstream.
"No Justice, No Peace," Dorsey typed under a Vine video loop he sent August 17, 2014, from Ferguson.
Dorsey was named Twitter CEO on Monday. The social network's outsize influence on our world is exemplified by his participation in the protests and other political causes, such as Amnesty International's Art for Amnesty program. On Tuesday, he tweeted a link to a Twitter "moment" -- a new feature on the service that displays short videos -- showing people assembling into a giant peace sign as part of Amnesty's commemoration of John Lennon's 75th birthday.
Nine-year-old Twitter has given voice to the silent, opened a new channel for marketers and built a virtual stage for entertainers. With just 316 million active monthly users -- a fifth of Facebook's 1.5 billion -- Twitter's power exceeds its size. Look no further than the Arab Spring movements that started five years ago, toppling governments in four countries and sparking protests and uprisings in a dozen more.
In Egypt, activists used Twitter to establish and distribute guidelines for confronting the government, the UK-based Guardian reported. San Francisco-based Twitter also helped draw worldwide attention to what was happening: Tweets jumped to 230,000 a day in the week leading up to Egyptian President Hosni Mubarak's ouster in early 2011, up from 2,300 a day, according to a University of Washington study.
"Twitter has become the digital town crier of our generation," said Richard Koci Hernandez, who teaches at the University of California at Berkeley's Graduate School of Journalism. "It's the fastest, most immediate way to spread a message."
Politics in 140 characters
Arguably, Twitter's most-profound influence has been on politics, where candidates and people in office now view it as the go-to platform for connecting with voters. Credit that perception to Barack Obama's 2008 presidential campaign, which showed the power of 140 well-chosen characters.
In an analysis of the 2012 presidential debate between Obama and Republican challenger Mitt Romney, a University of Wisconsin team found operatives from both campaigns used Twitter to shape voter opinions. The tactic was a sea change, said Christopher Wells, who led the study, because it broke from the traditional campaign practice of refining messages and sound bites on television news.
"The traditional spin room of debates has evolved into real time," Wells said.
The UK parliament has even issued a paper for its members that explains how they should use the service. Best practices include the advice, "Tell the truth, all the time" and "Talk less than you listen."
Tweeting as a new job category
Businesses have also been working to use Twitter as a marketing tool. Typing in the phrase "social media guru" on LinkedIn, for example, delivers almost 2,300 results. "Social media expert" returns more than 11,100 listings of people looking for jobs and companies seeking savvy professionals.
Companies' attempts to grab attention vary. Uniqlo, the Japanese fashion retailer, used Twitter to rope in shoppers during a campaign to celebrate its 26th anniversary. During the promotion, every 26th person who tweeted to the company got a 1,000 yen coupon.
In the UK, Domino's used Twitter to drive up deliveries of pepperoni pizzas by promising a discount based on how many tweets it received.
Market research firm eMarketer forecasts that companies worldwide will spend nearly $36 billion on social media campaigns, including Twitter, in 2017.
Twitter's use hasn't been without controversy. Sports leagues have fined athletes for tweets deemed to be in bad taste. Entertainers have engaged in long Twitter feuds. And sometimes it's well-known people just behaving badly.
Perhaps the most infamous example is former US Rep. Anthony Weiner's tweet of a link that led to a photo of his crotch. The resulting scandal effectively ended Weiner's political career.
"There isn't this divide that exists between their offline lives and their online lives," said Jesse Fox, a communication professor at Ohio State University. "The online world is in their pocket."
Others use Twitter for the fun of it.
Jimmy Fallon, the host of "The Tonight Show," has effectively outsourced writing for part of his late-night program by asking viewers to send funny stories about a specific topic, each with its own hashtag.
An account in the name of a cobra that escaped from the Bronx Zoo in 2011 narrates the snake's search for prey in New York City and has amassed more than 166,000 followers. The snake's proxy continues tweeting to this day.