Until this year, the most prominent American he had met was basketball star Dennis Rodman, with whom he struck up an unlikely friendship.

But in an abrupt turnaround, Singapore will host the first-ever meeting between a North Korean leader and a sitting US president, the climax of a series of summits in less than three months. Kim arrived Sunday for the event.

Last year Kim called Trump a "mentally deranged US dotard" but he now appears to have embraced a new diplomatic approach, coming across as polite and even charming in two meetings each with Chinese leader Xi Jinping and the South's President Moon Jae-in.

Family values

Kim is the third member of his dynasty to rule the Democratic People's Republic of Korea, as the country is officially known, and inherited power in 2011 when he was still in his 20s.

At the time he was considered untested, vulnerable and likely to be manipulated by senior figures. But he has established his authority over both the ruling Workers' Party and the military, proving his mettle by ruthlessly purging potential rivals.

The most senior victim was his uncle and mentor Jang Song-thaek, who was suddenly executed in 2013, denounced by state media as "despicable human scum" and proclaimed guilty of a variety of colourful crimes and political sins.

And last year his eldest half-brother Kim Jong-nam was brazenly assassinated in broad daylight, smeared with a deadly nerve agent as he walked through Kuala Lumpur's international airport in a hit which most analysts say could only have come from Pyongyang.

In contrast, his sister Kim Yo-jong has emerged as one of his closest advisers, constantly at his side during his diplomatic travels and acting as his envoy to the Winter Olympics in the South in February.

Eternal President

Rights groups say abuses are rampant in the North, where between 80,000 and 120,000 prisoners languish in political prison camps.

But Kim has also been keen to project a softer side, at least in official propaganda.

Unlike his father, who rarely smiled or spoke in public, the carefully vetted images of Kim Jong-un's heavily choreographed appearances show a more garrulous figure, laughing and joking with officers, soldiers and civilians during field trips, as well as giving speeches to packed halls of party functionaries.

He has noticeably modelled his image on that of his grandfather Kim Il-sung, appearing to mimic his hairstyle, dress, mannerisms and public speaking style.

Pyongyang is extremely sensitive and protective when it comes to the image of the ruling family, and Kim's father and grandfather are ubiquitous, their portraits adorning every home and office in the country while their bodies lie in state at the capital's Kumsusan Palace.

The North's founder Kim Il-sung remains the country's Eternal President despite having died in 1994, and the current leader's key governmental title is instead the unwieldy Chairman of the State Affairs Commission.

Lap of luxury

Unlike his grandfather, whose youth was dominated by the anti-Japanese struggle, Kim has led a life of luxury.

He was born to his father's third wife, Japan-born ethnic Korean dancer Ko Yong-hui, who is believed to have died of breast cancer in 2004.

Much of his early history is still surrounded in mystery -- so much so that even his precise date of birth is unclear.

He is said to have known that he would become North Korea's leader from his eighth birthday, when he received a general's uniform and the country's military top brass bowed to him.

Kim was sent to school in Switzerland, where he was looked after by his maternal aunt Ko Yong-suk and her husband.

School staff and friends, who were reportedly unaware that he was a member of North Korea's ruling family, remembered him as a shy boy who liked skiing, Hollywood tough guy Jean-Claude Van Damme and basketball.

Now, all eyes will be on the wily young leader as he meets the President of the United States. (AFP)