Greta Thunberg
Greta ThunbergREUTERS

US President Donald Trump responded to a tweet on Thursday morning congratulating 16-year old Swedish climate change activist Greta Thunberg for being named Times magazine's Person of the Year earlier this week.

"So ridiculous," Trump wrote on Twitter. "Greta must work on her Anger Management problem, then go to a good old fashioned movie with a friend! Chill Greta, Chill!"

Following Trump's tweet, Thunberg's Twitter bio was changed to include the president's remarks: "A teenager working on her anger management problem. Currently chilling and watching a good old fashioned movie with a friend."

Thunberg did the same after Brazilian president Jair Bolsonaro called her a brat on Tuesday after she condemned violence against indigenous people in Brazil.

"Greta said the Indians died because they were defending the Amazon (forest). How can the media give space to a brat like that," Bolsonaro said.

Thunberg subsequently changed her Twitter bio to "Pirralha" - the Portuguese word for a brat.

Trump previously tweeted about Thunberg in September after she spoke at the United Nations, writing sarcastically: "She seems like a very happy young girl looking forward to a bright and wonderful future. So nice to see!"

Thunberg is a controversial figure with supporters saying that she is making a valuable contribution to the issue of climate change with her outspokenness and fervency. Opponents assert that such a young girl without any expertise in the subject shouldn't be rebuking world leaders. Opponents also say she is simply a pawn of left-wing activists who are taking advantage of her naivete and youth for their own agenda.

Thunberg first heard about the issue of climate change when she was eight years old and became very anxious about the issue. Three years later, she suffered from severe depression and stopped talking and eating. She was later diagnosed with selective mutism, obsessive-compulsive disorder and Asperger syndrome.

Thunberg pressured her family to make changes to lower their carbon footprint. The family became vegan and her mother, who was an international opera singer, gave up her career due to Thunberg's opposition to flying.