Few expected Kim Jong Un to last long when he became the leader of North Korea in December 2011. His country was isolated and laboring under U.N. sanctions. The economy was in a shambles. To make matters worse, he had little experience running anything, let alone one of the world’s most oppressive governments. But the 27-year-old was no milksop. He was clever, ruthless and had more geostrategic nous than anybody had anticipated. Today, his grip on power is all but absolute.

The Great Successor, by Anna Fifield.

336 pages

PUBLICAFFAIRS, Nonfiction.

None of this was preordained. At least on paper, two other male siblings stood ahead in the line of succession. Another barrier was the Japanese roots of his mother, Ko Yong Hui. Though ethnically Korean, she was born in Osaka, where she was known as Hime Takada. Her family left when she was 10, along with over 93,000 other Korean migrants who, starting in 1959, followed Pyongyang’s entreaties to return and build the motherland.

Many would bitterly regret their decision, but Ko Yong Hui was luckier than most. As The Washington Post Beijing bureau chief Anna Fifield recounts in “The Great Successor,” her gripping first book, Ko Yong Hui was a gifted dancer who was able to join an elite state troupe. In the early 1970s, at a private performance, she caught the eye of Kim Jong Il, the future Dear Leader. Smart and ambitious, she became his favorite consort — his fourth — and a close advisor to boot. She never lost his affection and, when she died of cancer in 2004, the future of her children appeared secure. What was still unclear was who would actually succeed Kim Jong Il.

By then, one sibling had definitely been scratched off the list: Kim Jong Un’s older half-brother, Kim Jong Nam, the man who became an embarrassment when he was arrested attempting to visit Tokyo Disneyland in 2001, on a fake passport, using the alias “Fat Bear” — in 2017, Kim Jong Un would order his assassination for reasons that remain murky. The other contestant was Kim Jong Un’s older full brother, a languid sort of chap with a passion for guitars and Eric Clapton. Alas, he did not seem to have the killer instinct required. At the age of 20, Kim Jong Un seemed to offer the best hope for the continuation of the regime. After 2008, he was actively groomed for the job.

In many ways, he has been a transformational figure. Start with style: His shades-loving father was a sullen man who rarely uttered more than a few words in public. By comparison, Kim Jong Un smiles and laughs without restraint. He is often seen walking arm in arm with his glamorous young wife, Ri Sol Ju, a former singer of sundry all-girls bands. State media have shown him attending pop concerts, hosting the Harlem Globetrotters and even chatting with drunk-again-sober-again Dennis Rodman. The message to his people has been clear: This is a new era.

Style has been complemented with substance. One of the young despot’s most consequential decisions was to throw his full weight behind the development of private markets — his father had, at best, only tolerated them grudgingly. Today, across the country, from “the smallest of towns to the biggest of cities,” Fifield writes, “there’s at least one bustling marketplace.” U.N. sanctions notwithstanding, these have markedly improved the lives of North Koreans, and this largely explains why the regime has not collapsed despite the paranoia and brutality which, under Kim Jong Un, continues unabated.

Although “The Great Successor” is presented as a biography of Kim Jong Un, several chapters focus squarely on the country’s political, military and economic history. Fifield weaves that story skillfully, but she threads a well-reported path. The best parts by far — and those that make her book a must-read — cover the childhood and school years of the Kim children.

Take Kim Jong Un. From 1996, he spent more than four years in Switzerland, living in common-or-garden accommodation in the suburbs of Bern, under the care of his maternal aunt and her husband, who pretended to be his real parents. Fifield tracked them down — both later defected to the U.S. — along with old friends, school officials and principals, to reconstruct Kim Jong Un’s formative years.

The portrait that emerges is compelling. It is that of a child with a level of concentration bordering on the obsessive, but one who also became “short tempered and intolerant” in his teenage years. Early on, he developed a passion for machinery, especially model planes and ships. In Bern, he became crazy about basketball. When not on the court wearing his Chicago Bulls jersey and trash-talking the other team, he played the game compulsively on his PlayStation.

In North Korea, Kim Jong Un had grown isolated from other kids, even from his own half-siblings — his father kept the various branches of the family separate. No surprise then that he had trouble adapting to his new European milieu and that he was struggling with his studies. This was partly due to the language barrier: He was schooled in English for his first two years and then switched to an institution where instruction was in German. It did not help that he was away from school a lot, sometimes for as many as 100 days in a single year. One wonders how much he actually learned.

Fifield presents an equally persuasive picture of Kim Jong Nam, an admirer of the yakuza who sported large tattoos of a dragon and carp. Throughout, she peppers her brisk narrative with just the right dose of humor, irony and cynicism — it is hard to write about North Korea without any. At times though, she gets carried away — her frequent references to the Kim family as North Korea’s royalty can be distracting — but this does not affect the clarity of her message: We underestimate Kim Jong Un at our own peril.

A Q&A with author Anna Fifield can be read online at bit.ly/jtobooks.