Why it matters: "How dare you." Those three words, along with a pioneering school strike to protest climate change, catapulted 16-year-old Greta Thunberg into fame in 2019. She is now arguably the biggest voice on the world's biggest issue.
Along the way, she has faced criticism for delivering what some view as a naive and overly simplistic call to action. Others have commended her for showing bravery unseen by leaders three and four times her age. Whatever you think of her, one thing is clear: Greta Thunberg will be an essential player in the climate change debate for the considerable future.