Moon Jae-in is the man in the middle.
The South Korean president has become the mediator between Donald Trump and Kim Jong-un and is leading the diplomatic efforts to try to get North Korea to disarm.
Mr Moon's trip to Pyongyang on Tuesday, his third meeting with Mr Kim since April, may be his toughest challenge yet. He has to make real progress in persuading the North Koreans to make concrete steps to denuclearise. Otherwise the flurry of inter-Korean summits and the much-hyped Singapore meeting this year will be seen as glossy photo-ops, and President Trump may begin to lose patience.
With his approval rating dropping at home, Mr Moon needs a win. Here are some of the main obstacles he will need to overcome...
Making North Korea more convincing
President Trump declared in June, after meeting Mr Kim, that there was no longer a nuclear threat from North Korea.
But many believe North Korea has no intention of giving up its "treasured sword". Having spent decades developing nuclear weapons, why would it dismantle them?
The only commitment Kim Jong-un has made so far has been a vague pledge to "denuclearise the Korean peninsula". It lacks detail. That is something President Moon needs to change.
"I think it's incredibly important that the North Koreans offer some sort of symbolically and substantively significant concession this week in order to keep the South Korean public interested," says Andray Abrahamian, from the Griffith Asia Institute.
"Giving Moon a win would bolster his position domestically and put pressure on the United States to keep moving forward.
"In a real sense, we might see the two Koreas co-operating to nudge the United States forward in the process."
South Koreans who talked to Kim Jong-un earlier this month said he was frustrated that his promise to denuclearise was not being taken seriously by the international community.
If Mr Kim is serious then this summit is a good time to put it in writing, as many fear Mr Moon and President Trump are being manipulated and Chairman Kim is playing for time.
Senator Lindsey Graham, of South Carolina, told CBS's Face the Nation on Sunday: "If they're playing Trump, we're going to be in a world of hurt, because he's going to have no options left. This is the last, best chance for peace right here."
Keeping Trump in the loop
The White House argues that Mr Kim's last missile tests were 10 months ago - and that in itself is a sign of progress. However, satellite images appear to show North Korea is continuing to work on building weapons.
In public, the praise for Mr Kim continues to flow from the US president. After North Korea's military parade on the 9 September, Mr Trump thanked Chairman Kim for not showing off any missiles and said they would prove everyone wrong on denuclearisation.
In private, however, it's reported that many of his own administration are sceptical of North Korea's willingness to disarm. The split has been noticed in Pyongyang.
Andray Abrahamian believes Mr Kim is trying to skip "the gatekeepers that surround" Mr Trump. "There are risks there," he says.
"Washington DC is a politically unstable place right now and Pyongyang can't count on there being the same alignment of power in a few months down the road. That's another reason why it's important for them to find a breakthrough sooner rather than later."
President Moon has to keep both sides talking, and that means going straight to the source. After his meeting with the North Korean leader in Pyongyang, he will fly to the United Nations General Assembly to try to speak to Mr Trump.
Working out where to begin
Pyongyang and Washington are starting their negotiations from very different positions. That's why talks have stalled.
North Korea wants a declaration to end the Korean War. So does the South. The fighting finished in 1953 with an armistice and no peace treaty. At their summit in April, President Moon and Mr Kim signed a pledge to try to end the war by the end of this year.
But the US is not on board.
Washington wants North Korea to disarm first before it will negotiate a peace treaty. There are also concerns that such a declaration would give North Korea grounds to call for the removal of the 28,500 US troops stationed in South Korea. President Moon has been careful not to be critical of the Trump administration, but has called on both sides to take steps.
"There are ways to draft a declaration that is purely symbolic and does not affect US troops or interests in the region," says Duyeon Kim from the Centre for a New America Security.
"One way is to declare that the state of active war as it existed in the 1950s does not exist today, but that the armistice or key functions of the armistice agreement remains intact.
"This language would not have any legal implications for the UN Command and, in turn, US troops. It also does not legally or technically mean the North Korean threat has disappeared nor does it erase the rationale for America's deterrent in the region.
"But the key question is whether Pyongyang would be willing to agree on a declaration that upholds the armistice, or some of its key functions."
Mr Abrahamian says the win Mr Moon so badly needs from the talks does not necessarily need to be on the core issue of denuclearisation.
It could be "related to peace building and trust building", he says, like setting up a permanent centre for families divided by war, or pulling back artillery units from around the joint Korean business park at Kaesong.
Carrying the personal burden
President Moon's parents fled the North during the Korean War. He was one of 100,000 civilians in the Hungnam Evacuation, one of the US military's biggest-ever civilian rescues.
His mother gave birth to the future president in a refugee camp in Geoje, in present-day South Korea. His mother's sister did not make it onto a ship. In 2004 Mr Moon, then senior presidential secretary for civic and social affairs, travelled north with his mother to be reunited with his aunt in the tenth organised family reunions.
In South Korea, those who had to flee the North are called (실향민) "the people who lost their hometown". Some believe this personal experience is driving the South Korean president. Yang Hak-do, 85, was on a US cargo ship with Mr Moon's parents as they were taken to safety.
"Moon Jae-in must be carrying the burden of delivering his parents' wish - the wish to be buried back in hometown.
"I used to think that we shouldn't and couldn't talk with communists," he said. "But it seems like the North is changing little by little, and I am changing my thinking too that we should talk at least. I have a 50-50 split feeling questioning if the North is genuine and actually intends to change through conversation.
"Will they? But I am proud Moon is trying."