Kim Yo Jong's profile has been rising since 2014, when she was made deputy director of the Propaganda and Agitation Department of the Workers' Party. She and Kim Jong Un were born to the same mother, Ko Yong Hui.
Like most members of the Kim clan
, little is definitively known about Kim Yo Jong beyond her official rank. According to NK Leadership Watch
, she is a close aide of her brother's "and since his accession manages his public events, itineraries and logistical needs, among other tasks."
Kim Yo Jong was selected as an alternate member of the Political Bureau of the Central Committee of the Worker's Party at the Second Plenum of the party's 7th Central Committee.
Also in the reshuffle, according to state news agency KCNA, North Korean Foreign Minister Ri Yong Ho was selected as a member of the Politburo and Choe Ryong Hae, vice chairman of the Worker's Party and a close aide to Kim Jong Un, was appointed to the party's Central Military Commission.
Duyeon Kim, an analyst at the Korean Peninsula Future Forum, told CNN Kim's promotion of his sister "shows that he trusts her and that she is absolutely loyal to her brother."
"The whole slate of appointments and promotions he has made during the past meeting also shows that Kim Jong Un is trying to turn the Workers' Party into his party, into a Kim Jong Un party by filling senior positions and key positions with his people," she added.
The Politburo is the North Korean regime's top decision-making body, led by Kim Jong Un.
According to NK Leadership Watch
, a project of The US-Korea Institute, members and alternate members of the politburo can take part in debates and meetings, but only full members can vote.
A recent major decision by the Politburo was the expulsion in December 2013 of Kim's uncle and high-ranking party member Jang Song Thaek, who was later executed for treason
Born in 1987, Kim Yo Jong studied in Switzerland like her brother and is believed to have attended Kim Il Sung University and a western European school for her higher education.
"Since her brother's accession to the supreme leadership of (North Korea), Kim Yo Jong has been routinely observed attending Kim Jong Un's public appearances," NK Leadership Watch said.
Her position is such that, according to a Seoul-based think tank run by North Korean defectors, Kim Yo Jong briefly took charge of the country
while her brother was reportedly ill with gout or diabetes in late 2014.
Duyeon Kim said the continued promotion of his sister showed North Korea's leader was "trying to extend power and run the regime like a family dynasty, just like his father, just like his grandfather."
Nukes a 'powerful deterrent'
The key meeting of the Worker's Party comes amid an ongoing standoff between North Korea and the United States.
On Sunday, US President Donald Trump was critical of past attempts to reign in North Korea's missile and nuclear programs.
"Presidents and their administrations have been talking to North Korea for 25 years, agreements made and massive amounts of money paid ... hasn't worked, agreements violated before the ink was dry, makings fools of US negotiators," Trump wrote on Twitter
. "Sorry, but only one thing will work!"
In a speech Saturday, Kim Jong Un said the country's nuclear weapons "are a precious fruition borne by its people's bloody struggle for defending the destiny and sovereignty of the country from the protracted nuclear threats of the US imperialists."
North Korea has long defended its nuclear program as essential to defend the country against US aggression, pointing to the experience of countries like Iraq and Libya.
Nuclear weapons, Kim said, are a "powerful deterrent firmly safeguarding the peace and security in the Korean peninsula and Northeast Asia and reliably guaranteeing the Korean nation's sovereignty."
October 10 marks the founding anniversary of the Worker's Party. North Korea has in the past marked key dates with missile or nuclear tests.
Last week, Russian lawmaker Anton Morozov, recently returned from Pyongyang, told state media
preparations were underway for "new tests of a long-range missile."
Despite the pro-nuclear rhetoric, Kim's speech was also heavily focused on the economy, which has proven surprisingly resilient despite being heavily targeted by US and international sanctions
According to KCNA, Kim "noted with appreciation that the country's science and technology have developed by leaps and bounds and the national economy has grown on their strength this year, despite the escalating sanctions of the US imperialists and their vassal forces."
Advocates of dialog with North Korea have pointed
to increased economic ties as a potential avenue toward deescalation of tensions and improved relations both between North and South Korea and Pyongyang and Washington.