The faces behind 2015's influential hashtags

Social media has leveled the playing field, giving anyone the power to spread ideas, debunk propaganda, and even start social movements. In fact, the year 2015 saw several influential hashtags that reached beyond the realms of social media. Meet five people who started these movements: from stay-at-home dads to prime ministers.

#BlackLivesMatter - DeRay Mckesson

Newspapers have called #BlackLivesMatter "The most formidable American protest movement of the 21st century to date." Unlike some social media campaigns that fizzle-out after a few weeks, #BlackLivesMatter has morphed from a hashtag into a real political force.

That's due in no small part to activist DeRay Mckesson, who has become one of the movement's most recognizable faces. He not only spreads the movement's messages online but works on the ground too, leading protests, speaking at conventions and even meeting with US presidential candidates.

The 30-year-old activist began by live-tweeting from last fall's protests in Ferguson, Missouri after African-American teenager Michael Brown was shot and killed by white police officer Darren Wilson. He quickly became a leader in the grassroots movement, using the #BlackLivesMatter hashtag to organize the black community in the wake of several more police shootings. His up-front speaking style and his willingness to share personal details have helped him amass hundreds of thousands of followers.

#MyStealthyFreedom - Masih Alinejad

Sometimes, a single picture is all it takes to start a movement – especially when that photo features someone breaking the law.

That's what happened last May when Iranian journalist Masih Alinejad posted a photo of herself on Facebook without a headscarf. That's a big no-no in Iran, where women are required by law to wear a hijab in public. But when she asked her female Facebook friends if they'd ever broken the law, her timeline was flooded with similar photos.

Later in 2014, Ms. Alinejad started a Facebook page and a website called “My Stealthy Freedom,” a space for Iranian women to engage in this small act of public protest. And in just a few days her Facebook page had hundreds of thousands of followers and featured scores of pictures from women celebrating a brief moment of freedom without their headscarves.

Alinejad is continuing her activism while living in Great Britain and her movement is gaining momentum in Iran. She most recently supported two Iranian actresses who were banned from television and movies for posting photos without a hijab on their social media accounts.

#SelfieWithDaughter, #MakeinIndia, #WorldYogaDay, #DespiteBeingAWoman - Narendra Modi

Indian Prime Minister Narendra Modi, perhaps more than any other politician, has embraced the power of social media. He's quite good at it too.

Among world leaders, only Barack Obama (67 million) and Pope Francis (22 million across nine different language accounts) have more followers than Modi. And at times, it seems as if Modi is trending on Twitter all the time.

His own campaigns have made it to the top of Twitter's trending hashtag lists, including #SelfieWithDaughter, which encouraged parents to share photos with their daughters to celebrate women and girls; #MakeInIndia, his effort to promote Indian industry; and #WorldYogaDay, when Modi led tens of thousands of people in a mass outdoor yoga session.

Even his various gaffes have gone viral: most famously when he said Bangladesh Prime Minister Sheikh Hasina was tough on terrorism "despite being a woman." This inspired a barrage of creative backlash across the globe.

#IamAvijit - Avijit Roy

In some countries, posting controversial content on social media can get you in trouble, but in Bangladesh it can get you killed.

That was the sad fate of atheist blogger Avijit Roy. The Bangladeshi-American writer founded the Mukto-Mona ("Free Minds") blog, which hosted a community of activists. In February he traveled from his new home in the United States back to Bangladesh despite the threat of violence. He was later killed by hard-line Islamic militants.

His bravery to continue blogging in the face of danger inspired the hashtag #IamAvijit, a movement to defend free speech in Bangladesh, where free speech is technically legal, but atheism is a taboo. Sadly, the hashtag appeared multiple times this year in the wake of the murder of three more Bangladeshi atheist bloggers: Washiqur Rahman Babu, Ananta Bijoy Das and Niloy Chakrabarti. All three had been named on an online hit list.

Online freedom of speech is under threat in other countries as well. In Saudi Arabia, blogger Raif Badawi was sentenced last year to 10 years in prison and 1000 lashes for "insulting Islam" on his website, "Free Saudi Liberals." Badawi was given the 2015 Freedom of Speech award by Deutsche Welle.

#MH17- Eliot Higgins

In early 2012, Eliot Higgins was an unemployed stay-at-home dad. But today he's one of the Internet's most respected sleuths, piecing together facts about airstrikes, bombings and international wars.

Higgins gathers his information from social media, utilizing YouTube videos, tweets and geolocation data to investigate global conflicts. He has analyzed arms trafficking to Syria, the use of barrel bombs by the Assad regime, determined the location of "Islamic State" (IS) beheading videos and most recently tracked the targets of Russia's air campaign in Syria. But he made a name for himself investigating the downing of Malaysia Airlines flight MH17 last summer.

Higgins, with help from some of his Twitter followers, used YouTube videos to pinpoint the location of the missile launcher used to shoot down the passenger jet. He also gathered evidence suggesting the missiles originated in Russia.

His final conclusion: Russia was likely involved in the incident and the Kremlin's alternative theories were either deeply flawed or deliberately misleading.

His investigative work is often quicker than government investigators and, true to the spirit of social media, he makes it all publicly available on his website.