Her father transferred the young man to a provincial college to keep the two apart. But Ms. Kim hopped in her Soviet Volga sedan to see Mr. Jang each weekend.

Once they married in 1972, Mr. Jang’s career took off under the patronage of Kim Jong-il, his brother-in-law and the designated successor of the regime.

In his memoir, a Japanese sushi chef for Kim Jong-il from 1988 to 2001 who goes by the alias Kenji Fujimoto remembered Mr. Jang as a fun-loving prankster who was a regular at banquets that could last until morning or even stretch a few days. A key feature of the events was a “pleasure squad” of young, attractive women who would dance the cancan, sing American country songs or perform a striptease, according to the book and accounts by defectors.

Mr. Jang also mobilized North Korean diplomats abroad to import Danish dairy products, Black Sea caviar, French cognac and Japanese electronics — gifts Mr. Kim handed out during his parties to keep his elites loyal.

But North Korean diplomats who have defected to South Korea also said that during his frequent trips overseas to shop for Mr. Kim, Mr. Jang would drink heavily and speak dejectedly about people dying of hunger back home.

Few benefited more than Mr. Jang from the regime he loyally served. But he was never fully embraced by the Kim family because he was not blood kin. This “liminal existence” enabled him to see the absurdities of the regime more clearly than any other figure within it, Mr. Ra wrote.