Speculation and rumour about Kim Jong-un's health may amount to nothing, but questions about who might succeed him in the short or long term will always be there. The BBC spoke to analysts about the contenders and whether history is on their side.
A male member of the Kim family has been in charge of North Korea ever since its founding by Kim Il-sung in 1948 - and the mythology of this family runs deep throughout society.
Propaganda about its greatness begins for citizens before they can even read: pre-schoolers sing a song called: "I want to see our leader Kim Jong-un."
So how can you imagine a North Korea without this symbolic and political figure at the top? How would elites organise themselves, as well as society as a whole?
The easy answer is: we don't know. More interestingly, they don't know either. They have never had to do it.
As Kim Jong-un was being prepared for power, they even began using the term "Paektu Bloodline" to help legitimise his rule.
Paektu is the sacred and mythologised mountain where Kim Il-sung is said to have waged guerrilla war and where Kim Jong-il was reportedly born. Kim Jong-un still goes there when he wants to emphasise important policy decisions.
There has always been a Kim at the ideological heart of the country.
What would North Korea be like without such an heir? Kim Jong-un, 36, is believed to have children - but they are far too young. It is thought he has three children, the oldest being 10 and the youngest three. Kim Jong-un himself was considered young when he took power - he was 27.
It is likely that some sort of group leadership would emerge, perhaps as in Vietnam, that leans heavily on the founder's teachings and legitimacy to boost their own standing.
Observers can track who holds certain key positions and can follow news and open-source intelligence about important institutions, but can't really tell how factions are developing, nor who is holding power through personal rather than institutional bonds. Moreover, sometimes vice or deputy directors wield more real power than the titular heads of institutions. This makes all predictions extremely difficult.
The three remaining Kims
The are three Kims who could potentially be involved in the political make-up of North Korea if Kim Jong-un were to disappear. They all face limitations in carrying on family rule.
The first is Kim Yo-jong, Kim Jong-un's younger sister. She is said to have been a favourite of her father who commented on her precocity, her interest in politics from a young age. Her manner is efficient, mild and one suspects rather observant. Much has been made of her closeness to her brother. At the Singapore Trump-Kim summit she was famously on hand to pass him a pen to sign the agreement with, and at the next summit in Hanoi, was pictured peeking out from behind corners as her brother posed for statesman-like photos.
Yet she was not above a temporary demotion after the Hanoi summit - purportedly because of its failure although this will never be confirmed. She doesn't sit on the top policy-making body, the State Affairs Commission, but is an alternate member of the Politburo and vice director of the Propaganda and Agitation Department (PAD) of the Workers' Party of Korea. These may seem like incomprehensible acronyms but the PAD is a powerful organisation that ensures ideological loyalty in the system.
She is a woman, however, and this makes it hard to imagine her occupying the top position in such a deeply patriarchal country. North Korea is an extremely male state, in which gender carries rigid expectations. Being supreme leader, and certainly running the military, does not fit in the range of womanly duties.
The second is Kim Jong-chul. He is Kim Jong-un's older brother, but has never appeared interested in politics or power. (He is known to be interested in Eric Clapton.) At most, he could be a symbolic link to the Kim family: perhaps made the head of a foundation and put forward to read the odd speech.
The final one is Kim Pyong-il, Kim Jong-il's half-brother. His mother - Kim Jong-il's stepmother - was angling to have him become Kim Il-sung's successor. She failed and was sidelined by Kim Jong-il as he rose in influence. Kim Pyong-il was sent to Europe in 1979, where he has held various ambassadorships, returning to North Korea only last year. This means it is very unlikely he has the network to be a central player in elite politics in Pyongyang.
The second-most powerful man in North Korea right now
There are other individuals who have been central in the Kim Jong-un era, but it is difficult to know who among them would form co-operative relationships and who would compete with one another.
One is Choe Ryong-hae. He has had his ups and downs under Kim Jong-un, but having weathered a few storms currently sits on the presidium of the politburo and is also first vice chairman of the State Affairs Commission. Last year he became the first new president in 20 years, replacing the aging Kim Yong-nam - so he is the person who represents the North at international engagements.
Choe has also held high positions in the military and the Organization and Guidance Department (OGD) of the Worker's Party of Korea, responsible for enforcing loyalty throughout the regime. This is an extremely powerful organisation: it enforces the adherence of all citizens to North Korea's ideology. He is probably the second most powerful man in North Korea.
The old spymasters and rising political grandees
Another is Kim Yong-chol. This general paved the way for the Trump-Kim summits, meeting US Secretary of State Mike Pompeo several times. He has been head of the United Front Department (responsible for relations with South Korea) and the Reconnaissance General Bureau, the country's main intelligence service. He seems to have suffered a demotion following the collapse talks with the United States, but it is unlikely this spymaster will remain obscure for long.
Yet another is Kim Jae-ryong. As well as being on the State Affairs Commission, he is Premier of the Cabinet, a moderately influential position. Relatively little is known about him, but his star has risen in the past years as others have fallen. He is known for managing industries and ran the most isolated province, home to key military-industrial sites, for several years. This may mean he has been closely involved in the nuclear program.
Jong Kyong-taek is responsible for the State Security Department, which investigates and punishes political crimes. It also helps physically protect the leadership. These are crucial responsibilities that help enforce stability in the system.
Hwang Pyong-so is another official who has held top military posts and has run the OGD in the Kim Jong-un era. Like Choe (and many others) he has been disciplined; he doesn't seem to have been rehabilitated in the same way, however. Other 2010s foreign policy stalwarts Ri Yong-ho and Ri Su-yong have also seen roles diminish recently. They have been replaced by Ri Son-gwon and Kim Hyung-jun. The former is said to be an ally of Kim Yong-chol.
The military enforcers
A handful of top generals of the Korean People's Army (KPA) would also certainly exert influence in any transition period. Currently, two men sit atop the General Political Bureau of the KPA, Kim Su-gil and Kim Won-hong. This bureau enforces political loyalty in the military, something that would be absolutely crucial during periods of uncertainty.
Kim Won-hong, helps illustrate how difficult it is to predict how power would be shared if Kim Jong-un were no longer there. Kim Won-hong and Hwang Pyong-so had been thought to be rivals, competing to influence Kim Jong-un at the other's expense.
Amongst top elites, who would clash and who would ally? Would there be pro and anti-Kim Yo-jong factions? Would the fear of instability stop rivalries from getting out of hand? After all, it is in no elite politician's interest to see the state collapse, opening the door for some kind of takeover by South Korea, or even China.
There is currently no perfect contender: his sister would have to overcome the sexism and the break from tradition of a male heir. Anybody else is not directly descended from that all-important Paektu bloodline. but in the end, they will all have to think of the unity of the state they have defied every international norm to preserve.