The sombre, subdued and rounded figure that was often the subject of international ridicule in those early days has now made North Korea a global threat in a way his father Kim Jong-il never did.
Kim Jong-un also did what no previous North Korean leader could - bring a sitting American president to the negotiating table.
But historic talks with the former US President Donald Trump and early moves to improve relations with the South led nowhere eventually.
Pyongyang's relationship with Washington and Seoul has since soured and turned increasingly volatile.
In November, the North fired at least 23 missiles, the most it has ever launched in a day, including one that landed less than 60km off the South's city of Sokcho - the closest a North Korean missile has come to South Korea's territorial waters.
Under Kim Jong-un, in 2022 alone, Pyongyang tested a record number of missiles, aimed two ballistic missiles over Japan, and has continued preparing for a seventh nuclear - one that analysts expect despite dire warnings from the US, South Korea and Japan.
'Morning Star King'
Soon after Kim Jong-un, the youngest son of Kim Jong-il and his third wife Ko Yong-hui, was born in 1983 or 1984, a state-sanctioned personality cult swung into action.
Mythology claimed that the Kims were a semi-divine dynasty who had a close affinity with the near-sacred Mount Paektu that sits on the Korean-Chinese border.
By that logic, the young Kim would be naturally endowed with heroic qualities and preternatural strength. In fact when he was announced as the leader in 2011, the pronouncement made clear that he "inherits the ideology, leadership, courage and audacity of [his father] Comrade Kim Jong-il".
Audacity was not an inappropriate word to use: within five years of coming to power, he had executed his uncle, is widely believed to have ordered the assassination of his half-brother in a Kuala Lumpur airport, and North Korea claimed it had developed a hydrogen bomb that could be mounted in an inter-continental ballistic missile (ICBM).
Kim Jong-un had little political or military experience, but almost immediately after the death of his father, he was hailed as "the great successor". He was also named head of the party, state and army, and took on the mantle of North Korea's Supreme Leader.
He was initially not thought to be able to take up his father's mantle. Analysts focused instead on his older brother Kim Jong-chol and older half-brother Kim Jong-nam.
But Kim Jong-nam's deportation from Japan in May 2001 and Kim Jong-chol's reported "unmanliness" improved the younger Kim's chances.
Analysts saw him as the heir-to-be after he was awarded a series of high-profile political posts.
Swiss-educated like his brothers, Kim Jong-un avoided Western influence, returning home when not in school and dining out with the North Korean ambassador.