From producing an ashtray during a cigarette break en route to a nuclear summit to issuing a statement in praise of the US president, Kim Yo-jong has become the single most important figure in the North Korean regime after her brother, the country’s leader, Kim Jong-un.

Since representing Kim at the 2018 Winter Olympics in Pyeongchang, South Korea, Yo-jong has not only acquired prestigious titles within the ruling Workers’ party. She is rumoured to be the brains behind Kim’s carefully constructed public image, at home and abroad. In return, she enjoys the absolute confidence of her brother, a leader capable of ordering the execution of his own uncle for alleged treason.

As the world grapples with the coronavirus pandemic – with Pyongyang continuing to insist it has not recorded a single case – Kim Yo-jong’s ascendancy continues.

Last month, she made her first public statement, condemning the South as a “frightened dog barking” after Seoul protested against a live-fire military exercise by the North. And in March, she publicly praised Donald Trump for sending Kim a letter in which he said he hoped to maintain good bilateral relations and offered help in dealing with the coronavirus pandemic.

The publication of political statements in Kim Yo-jong’s name underlines her central role in the regime, according to Youngshik Bong, a research fellow at Yonsei University’s Institute for North Korean Studies in Seoul. “It is revealing that Kim Jong-un permitted her to write and announce a scathing statement about South Korea in such a personal tone,” Bong said. “He is clearly ready to allow his sister to become his alter ego.”

Facebook Twitter Pinterest Kim Yo-jong in Seoul with the South Korean president, Moon Jae-in, in 2018. Photograph: KCNA/EPA

But Yo-jong, who accompanied Kim to his two summits with Trump, apparently paid a price when his nuclear diplomacy suffered a setback. Last weekend, she was reinstated to the party’s powerful politburo, according to the state Korean Central News Agency, just over a year after she had reportedly been removed from the position and told to keep a low profile following the failure of the Hanoi denuclearisation summit.

And she has not escaped the attention of US officials, who in 2017 placed her and other North Korean officials on a blacklist for “severe human rights abuses”.

Internationally, Yo-jong has been a visible presence throughout the regime’s high-stakes diplomatic process with Washington and Seoul. At home, she has performed the role of propagandist-in-chief, burnishing Kim’s reputation as head of the dynasty that has ruled North Korea for three generations.

“She has direct access to and strong influence on Kim Jong-un,” said Leonid Petrov, a North Korea specialist and senior lecturer at the International College of Management in Sydney. “She is not associated with his purges or military brinkmanship, but knows all about them. She is a trusted political figure who helps Kim maintain a positive public image when he is dealing with foreigners or South Koreans.”

Facebook Twitter Pinterest Kim Yo-jong with her brother at a meeting with Moon Jae-in in the demilitarised zone in 2018. Photograph: Reuters

Yo-jong, who is thought to be four years younger than her brother, was rarely seen in public until 2010, when she was photographed attending a party conference. By the following year, she was a regular presence in her father Kim Jong-il’s entourage, and was seen mourning after his death in late 2011.

But her journey to the heart of the North Korean regime had arguably begun in the late 1990s, when she attended primary school in Berne, Switzerland at the same time as Kim Jong-un, with whom she lived in a private home, attended to by staff and watched over by bodyguards, according to North Korea Leadership Watch.

“They were virtually in exile together, both knowing what the future had in store for them,” Bong said. “They must have gained a tremendous sense of having a common fate. As a result, she has her brother’s unconditional trust.”

Little is known about Yo-jong’s life during the period between her graduation with a computer science degree from Kim Il-sung University in Pyongyang and 2007, when she began to play a junior role in the ruling party.

She is said to have been involved in arranging her brother’s succession as supreme leader after Kim Jong-il suffered two strokes in 2008, but was not mentioned by North Korean state media until March 2014, when she accompanied her brother during elections for the Supreme People’s Assembly.

“The North Korean regime is a family business, and Kim Jong-un appears to place trust in his sister,” said Leif-Eric Easley, associate professor of international studies at Ewha University in Seoul. “She has demonstrated skills at modernising the brand of the regime, and has some sway over state propaganda. Her most important function is probably as a confidante to her brother.

“But she also has a signalling role because messages from Kim Yo-jong carry more weight than those of an imminently replaceable North Korean official.”

Kim Yo-jong’s upward trajectory is expected to continue once the North resumes its nuclear diplomacy in a post-pandemic world. “She plays a pivotal role in North Korean domestic and foreign policy campaigns because she is one of the main stakeholders in the regime’s survival,” Petrov said.

But, he added, she would never adopt the mantle of leader should something happen to her brother. “Kim Yo-jong knows how to smooth Kim Jong-un’s initiatives and strengthen his soft power … but she won’t replace the primary decision-maker. North Korea is a Confucian country where seniority and masculinity are respected. She is Kim’s most trusted ally, but no more than that.”