Young climate activist Greta Thunberg has stared down Donald Trump during a chance encounter in New York before she went on to give the world’s most powerful leaders a sensational serve.

Just over 13 months ago, a 15-year-old schoolgirl was sitting alone in front of the Swedish Parliament, pink backpack to one side and on the other, a simple handwritten sign reading, “Skolstrejk for Klimatet.”

It was August 20, 2018, and luckily for Greta Thunberg, PR guru Ingmar Rentzhog happened to be strolling past “on the way to work”. Mr Rentzhog, founder of green social network start-up We Don’t Have Time, was moved to see Ms Thunberg striking “alone against the whole world”.

That day, Mr Rentzhog posted the now-iconic image of Ms Thunberg to Instagram and Facebook, describing her protest and relaying the message from her flyers. “We kids usually don’t do what you tell us to do,” it said. “We do as you do. And since you grown-ups don’t give a shit about my future, I won’t either.”

Almost simultaneously, the young climate activist posted the same message to her Twitter account — where today she has more than 1.8 million followers as leader of what has become a global youth movement.

In the space of a year, Ms Thunberg has gone from her lone protest to speaking at Davos, the European Union, the US Congress and this week the United Nations, on the heels of last Friday’s marches in cities across the world.

In his Facebook post last August, Mr Rentzhog wrote, “Her school strike starts today and continues until election day. She sits in front of Parliament House. During the time I was there, only one passer-by came forward and took her info sheet. No one except me talked to her!”

Jag vill dela med mig av en väldigt känslosam morgon. Dagen börjar med lämning av min 3-åriga son på sin nya... Posted by Ingmar Rentzhog on Monday, 20 August 2018

Despite its name, We Don’t Have Time did have time to produce a short film about Ms Thunberg, which it posted to Facebook the next day. The story took off like wildfire, quickly going viral in Swedish and international media.

“We Don’t Have Time reported on Greta’s strike on its first day and in less than 24 hours our Facebook posts and tweets received over 20,000 likes, shares and comments,” the company wrote in a post on Medium on August 23.

“It didn’t take long for national media to catch on. As of the first week of the strike, at least six major daily newspapers, as well as Swedish and Danish national TV, have interviewed Greta. Two Swedish party leaders have stopped by to talk to her as well.”

That day, newspaper Dagens Nyheter published a feature interview with Ms Thunberg’s parents, opera singer Malena Ernman and actor Svante Thunberg, about their new book, a family memoir titled Scenes from the Heart.

It was in that book — which described the climate activist’s childhood but was written largely before the family came to public attention — that Ms Thunberg’s mother famously described the teenager’s Asperger’s syndrome as a “superpower”.

Swedish journalist Andreas Henriksson was the first to point out that Mr Rentzhog likely already knew Ms Thunberg and her family, having taken part in the same climate change conference in May that year.

Mr Rentzhog later took to Facebook to clarify that it was “no secret” he had helped Ms Thunberg with PR but that he had not been involved in planning the climate strike. He said he had received a “tip” that there would be a protest outside parliament, but what did “not expect” was that it would “consist of a single 15-year-old girl”.

Ms Thunberg also addressed the issue directly in February this year, writing on Facebook that the climate strike was entirely her idea and even her parents “weren’t very fond of it”. “On the 20th of August I sat down outside the Swedish Parliament,” she wrote.

“I handed out flyers with a long list of facts about the climate crisis and explanations on why I was striking. The first thing I did was to post on Twitter and Instagram what I was doing and it soon went viral. Then journalists and newspapers started to come.”

Recently I’ve seen many rumors circulating about me and enormous amounts of hate. This is no surprise to me. I know that... Posted by Greta Thunberg on Saturday, 2 February 2019

She continued, “A Swedish entrepreneur and businessman active in the climate movement, Ingmar Rentzhog, was among the first to arrive. He spoke with me and took pictures that he posted on Facebook. That was the first time I had ever met or spoken with him. I had not communicated or encountered him ever before.”

Ms Thunberg said people “love to spread rumours saying that I have people ‘behind me’ or that I’m being ‘paid’ or ‘used’ to do what I’m doing” but that “there is no one ‘behind’ me except for myself”.

“My parents were as far from climate activists as possible before I made them aware of the situation,” she said.

“I am not part of any organisation. I sometimes support and co-operate with several NGOs that work with the climate and environment. But I am absolutely independent and I only represent myself. And I do what I do completely for free, I have not received any money or any promise of future payments in any form at all. And nor has anyone linked to me or my family done so.”

Late last year, Mr Rentzhog was accused of using Ms Thunberg’s name to raise more than $1.5 million (10 million SEK) from investors in the company, which donates just 10 per cent of its profits to a charitable fund.

In October, he had asked her to sit on the Youth Advisory Board of We Don’t Have Time. He then used her name more than 11 times in promotional materials for a share issue announced on November 27, Svenska Dagbladet reported.

According to the newspaper, the prospectus promised investors the company could be “extremely profitable” by creating viral environmental content to pull in money via digital ads from green-aligned firms.

Ms Thunberg’s father told Svenska Dagbladet that Mr Rentzhog had never informed the family her name would be used. “No, we haven’t received any information about that. Neither has Greta,” he said. “It is unfortunate if she was used commercially. But she hasn’t known anything about this. None of us have known this.”

In a statement in February, the company — which is aiming to build a climate-oriented social network with 100 million users — said it rejected accusations of exploiting Ms Thunberg but apologised for “miscommunication”.

“We failed to inform the Thunberg family in advance that Greta would be mentioned in our financial prospectus, a document aimed at raising funds for the company,” Mr Rentzhog said in the statement.

“A prospectus is required by law to present a fair and accurate view of operations, but we’re very sorry that we didn’t inform them of this. I’ve spoken to the family and they’ve accepted our heartfelt apology for this mistake.”

In a subsequent interview with The Local, Mr Rentzhog defended his company against claims of “eco-profiteering”. “If my interest were to earn money, I should have stayed in my old company, because this is much, much higher risk,” he said. “It’s not money which is driving me.”

Ms Thunberg stepped down from the company’s Youth Advisory Board in the wake of the revelations, but Mr Rentzhog told the website it was not because of any clash but because “she must focus 100 per cent of the time on her own thing, because she’s probably the most busy 16-year-old girl out there in the world”.

Though it’s unclear whether Mr Rentzhog and Ms Thunberg have a formal business arrangement, the PR manager continues to promote her work. Just a few days ago he shared a post on Facebook that featured Ms Thunberg arguing the need to restore natural carbon sinks a short film about helping “tackle the climate crisis”.

This week, Ms Thunberg’s profile was given its biggest boost yet with a fiery address to world leaders at the United Nations Climate Action Summit in New York.

During her speech on Monday, the teenager accused leaders of ignoring climate change, telling them they had “stolen my dreams and my childhood”. “How dare you,” she said. “People are suffering. People are dying. Entire ecosystems are collapsing.”

US President Donald Trump, who pointedly ignored Ms Thunberg as he arrived at the UN, later shared a video of her tearful speech with a mocking tweet, “She seems like a very happy young girl looking forward to a bright and wonderful future. So nice to see!”

frank.chung@news.com.au