The Kim's are generally portrayed in the US media as ruthless cold blooded dictators who repress their populace. It's widely known that there is widespread lack of food in North Korea. But how much of this starvation is due to the Kim rulers and how much is due to international sanctions?
This is a broad topic, and placing blame for such a complex issue is difficult (see the comments), especially when you are not restricting the question to any timeframe.
But according to this UN report, the North Korean leadership is responsible for "the death of at least hundreds of thousands of people" because of a lack of access to food:
The State has used food as a means of control over the population. It has prioritized those whom the authorities believe to be crucial in maintaining the regime over those deemed expendable. [...]
Even during the worst period of mass starvation, the State impeded the delivery of food aid by imposing conditions that were not based on humanitarian considerations. [...]
The State has consistently failed in its obligation to use the maximum of its available resources to feed those who are hungry. Military spending – predominantly on hardware and the development of weapons systems and the nuclear programme – has always been prioritized, even during periods of mass starvation. [...] Large amounts of State resources, including parallel funds directly controlled by the Supreme Leader, have been spent on luxury goods and the advancement of his personality cult instead of providing food to the starving general population. [...]
The State has also used deliberate starvation as a means of control and punishment in detention facilities. This has resulted in the deaths of many political and ordinary prisoners. [...]
While acknowledging the impact of factors beyond State control over the food situation, the commission finds that decisions, actions and omissions by the State and its leadership caused the death of at least hundreds of thousands of people [...]
While conditions have changed since the 1990s, hunger and malnutrition continue to be widespread. Deaths from starvation continue to be reported. The commission is concerned that structural issues, including laws and policies that violate the right to adequate food and freedom from hunger, remain in place, which could lead to the recurrence of mass starvation.
See also wikipedia.
It should be noted that starvation is not the only human rights issue. It's not only the US media that represents North Korean leaders as "ruthless cold blooded dictators who repress their populace". See eg the summary of the previous UN report:
These crimes against humanity entail extermination, murder, enslavement, torture, imprisonment, rape, forced abortions and other sexual violence, persecution on political, religious, racial and gender grounds, the forcible transfer of populations, the enforced disappearance of persons and the inhumane act of knowingly causing prolonged starvation
See also: Human rights in North Korea
Socialism and Communism have a long history of causing famines. Most notable are the Great Chinese Famine and the Soviet Famine of 1932-3. More recently, we have people dying of hunger in Venezuela. Not quite a famine, at least not yet. The Kims could easily have prevented the famine by switching to a Capitalist system. But then they wouldn't get to be dictators.
EDIT: Since people seem to object that I haven't shown causation, a bunch of points. First of all, South Korea was experiencing an economic boom at the time. The difference between North and South Korea was that one was Communist and the other was Capitalist. Secondly, US and other sanctions didn't stop North Korean trade with China, which was in the process of abandoning Communism in all but name. So if you are going to blame sanctions, you are asserting that trade with the Western world is somehow magical; trade with China was apparently not sufficient.
Thirdly, the North/South Korea contrast is part of a pattern. Finland and Eastern Poland were part of the Russian Empire but not part of the USSR. The USSR had multiple famines in the 1920s and 1930s; Finland and Eastern Poland didn't. Taiwan was part of China before the Communist revolution. China had a famine after the split; Taiwan didn't. In South America today, only Venezuela is hardcore socialist, and only Venezuela is in a condition of near-famine.
The upshot is that we have a repeated experiment, where regions that are either politically similar (as in South America) or even part of the same political unit (as in Korea, the Russian Empire, and China) split up, with part going Communist and part not. In cases where one region has a famine and the other doesn't, the famine region is always the Socialist or Communist one. By contrast, I am unable to locate a single example where a region split in this way, the Capitalist one had a famine, and the Communist one didn't.
As the other answer explains, attributing causation is difficult. But when you have a repeated experiment with a repeated result, it gets a lot easier. And that's the case here.
Further edit: Just ran across this. Looks like the postwar USSR would also have had a hunger problem were it not for their grain imports. And Russia today is a major grain exporter. So is Ukraine. And Kazakhstan. All just a coincidence?