Greta Thunberg was born 3 January 2003 and is a Swedish teenage environmental activist on climate change whose campaigning has gained international recognition. Thunberg says she first heard about climate change in 2011 when she was 8 years old, and could not understand why so little was being done about it. Three years later she became depressed, lethargic, and stopped talking as well as eating. She was eventually diagnosed with Asperger syndrome, obsessive–compulsive disorder (OCD), and selective mutism. While acknowledging that her diagnosis "has limited me before", she does not view her Asperger's as an illness and has instead called it her "superpower".

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Thunberg first became known for her activism in August 2018 when, at age 15, she began spending her school days outside the Swedish parliament to call for stronger action on global warming by holding up a sign saying in Swedish with the words "School strike for climate". Soon, other students engaged in similar protests in their own communities. Together, they organized a school climate strike movement under the name "Fridays for Future". After Thunberg addressed the 2018 United Nations Climate Change Conference, student strikes took place every week somewhere in the world. In 2019, there were at least two coordinated multi-city protests involving over one million students each.

Thunberg is known for her blunt, straightforward speaking manner, both in public and to political leaders and assemblies in which she urges immediate action to address what she describes as the climate crisis. At home, Thunberg convinced her parents to adopt several lifestyle choices to reduce their own carbon footprint, including giving up air travel and not eating meat. Her mother is an opera singer and her father a film actor and both now restrict their professional appearances to only Sweden. Both have become vegans as their daughter's urging.

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Her sudden rise to world fame has made her a leader and a target. In May 2019, Thunberg was featured on the cover of Time magazine, which named her a "next-generation leader" and noted that many see her as a role model. Thunberg and the school strike movement were also featured in a 30-minute Vice documentary titled Make the World Greta Again.

Some media have described her impact on the world stage as the "Greta Thunberg effect". Thunberg has been the recipient of numerous honors and awards, including fellowship of the Royal Scottish Geographical Society, which has been named as one of the 100 most influential people of 2019 by Time magazine. Thunberg was nominated for the 2019 Nobel Peace Prize which was ultimately awarded to Ethiopian Prime Minister Abiy Ahmed Ali. In September 2019, she addressed the UN Climate Action Summit in New York. She is currently in Canada addressing a number of halt climate change rallies, traveling in a Tesla and refusing to fly or take any transportation that produces greenhouse emissions.