Even Kim Yo Jong's age is a mystery. She's rumored to be 36 years old, approximately four years younger than her brother, and reportedly is the youngest child of former leader Kim Jong Il.
Her first public appearance was at her father's funeral in 2011. Since then, she has worked quietly in the background of Kim Jong Un's regime, even accompanying him in 2018 as he met South Korean leader Moon Jae-in during the historic summit between the two nations.
Just months beforehand, she attended the Winter Olympics in Pyeongchang, South Korea, becoming the first member of North Korea's ruling family to visit the region since the end of the Korean War in 1953. She later attended a highly publicized lunch with Moon Jae-in.
Kim Yo Jong would be the first woman to rule over North Korea which has built up its nuclear stronghold despite the rest of the country living in poverty.
Seoul repeatedly has denied that Kim Jong Un's health was in dire peril, even as unconfirmed rumors and media reports suggested he was in a vegetative state after undergoing heart surgery.
Kim Yo Jong's reputation has suggested she would rule much in the vein of her brother, who has represented the third generation of their family to lead North Korea.
In a rare public statement this past March, she criticized South Korea's presidential Blue House for urging North Korea to cease nuclear-weapons testing in an effort to quell tensions in the region.
Kim Yo Jong currently has served as the first vice-department director of the Workers Party's Central Committee.
U.S. officials placed her on a blacklist in 2017 for human-rights abuses.