AP Photo

SEOUL, South Korea — There is only one photograph available outside North Korea thought to be that of the man South Korean officials believe will inherit the world’s most unpredictable regime, one that is armed with nuclear weapons. In that picture, the man, Kim Jong-un, a son of the ailing North Korean leader, Kim Jong-il, is an 11-year-old.

There is only one photograph available outside North Korea of Kim Jong-un; it is of him as an 11-year-old with a bratty grin.

“When Prince Jong-un shook hands with me, he fixed me with a vicious look,” Kim Jong-il’s former Japanese sushi chef wrote in a 2003 memoir describing his first encounter with the boy, then 7, dressed in a military uniform and known as a “prince” among his father’s aides. “I...