Greta Thunberg, the Swedish schoolgirl who inspired a global movement to fight climate change, has been named Time magazine's Person of the Year for 2019.
The 16-year-old is the youngest person to be chosen by the magazine in a tradition that started in 1927.
Speaking at a UN climate change summit in Madrid before the announcement, she urged world leaders to stop using "creative PR" to avoid real action.
The next decade would define the planet's future, she said.
Last year, the teenager started an environmental strike by missing lessons most Fridays to protest outside the Swedish parliament building. It sparked a worldwide movement that became popular with the hashtag #FridaysForFuture.
Since then, she has become a strong voice for action on climate change, inspiring millions of students to join protests around the world. Earlier this year, she was nominated as a candidate for the Nobel Peace Prize.
At the UN Climate Conference in New York in September, she blasted politicians for relying on young people for answers to climate change. In a now-famous speech, she said: "You have stolen my dreams and my childhood with your empty words. We'll be watching you."
Reacting to the nomination on Twitter, the activist said: "Wow, this is unbelievable! I share this great honour with everyone in the #FridaysForFuture movement and climate activists everywhere."
The teenager's message, however, has not been well received by everyone, most notably prominent conservative voices. Before her appearance in Madrid, Brazil's President Jair Bolsonaro called her a "brat" after she expressed concern about the killing of indigenous Brazilians in the Amazon.
"Greta said that the Indians died because they were defending the Amazon," Mr Bolsonaro told reporters. "It's impressive that the press is giving space to a brat like that," he said, using the Portuguese word for brat, "pirralha".
The activist responded by briefly changing her Twitter bio to "Pirralha".
She has previously been at odds with US President Donald Trump, who has questioned climate science and rolled back many US climate laws, and Russian President Vladimir Putin, who once called her a "kind but poorly informed teenager".
Announcing Time's decision on NBC, editor-in-chief Edward Felsenthal said: "She became the biggest voice on the biggest issue facing the planet this year, coming from essentially nowhere to lead a worldwide movement."
The magazine's tradition, which started as Man of the Year, recognises the person who "for better or for worse... has done the most to influence the events of the year". Last year, it named murdered and imprisoned journalists, calling them "The Guardians".
What happened in Madrid?
At the COP25 Climate Conference in Madrid, Greta Thunberg accused world powers of making constant attempts "to negotiate loopholes and to avoid raising their ambition".
"The real danger is when politicians and CEOs are making it look like real action is happening when, in fact, almost nothing is being done apart from clever accounting and creative PR," she said, drawing applause.
"In just three weeks we'll enter a new decade, a decade that will define our future," she added. "Right now, we're desperate for any sign of hope."