What happens to economic reforms?
"Jang Song Thaek is a person who at one point Kim Jong Un had to cut out as he solidifies his own power structure," said Koh Yu-hwan of Dongguk University in Seoul, a leading expert on the North's leadership.
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"I think the young elite had Kim get rid of Jang, meaning that he will rule without a guardian."
Accordion-playing Jang, 67, is married to Kim Jong Un's aunt, Kyong Hui, who is a daughter of the North's founding leader and its "eternal President", Kim Il Sung.
Jang, who is widely seen as an advocate of economic reform, was purged in a power struggle in 2004 under Kim Jong Il's rule but was reinstated two years later.
One key question now is what his ouster will mean for the devastated economy.
"Within the current leadership, he (Jang) seems to be the face of economic reform, so there is a risk involved with removing someone that close to the program," said John Swenson-Wright, a senior fellow at Chatham House, a London-based international affairs think tank.
Earlier this year, Jang and his wife were seen backing the appointment of Pak Pong Ju, a career technocrat, for the post of premier to spearhead a push to improve the economy.
Jang has been the central figure among top officials and family members who worked to ensure the young and untested son of Kim Jong Il took over power when his father died in 2011.
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While Jang's ouster could symbolically tip the balance of power in favor of a key figure in the military, Choe, analysts say it is unlikely to signal a return to the military grandstanding of Kim's father as a top priority.
Apart from domestic political problems, North Korea is involved in a protracted standoff with the West over its nuclear weapons program.
Tensions between North and South Korea soared earlier this year as Pyongyang reacted angrily to tightened U.N. sanctions imposed in response to its latest nuclear test, but then eased for several months. The two sides are still technically at war after their 1950-53 civil war ended in a mere truce, not a treaty.