The president was grappling with a slowing economy, a deadly crowd crush and nuclear threats from a belligerent neighbor. Then came a much more personal scandal: spy cam footage that showed his wife accepting a $2,200 Dior pouch as a gift.

It has quickly escalated into one of the biggest political crises for President Yoon Suk Yeol of South Korea, who has made his mark in foreign policy by aligning his country more closely with the United States and Japan but has been bogged down by controversies at home, many of them involving the first lady, Kim Keon Hee.

The video of Ms. Kim, which emerged late last year, has caused a rift between Mr. Yoon and one of his most trusted lieutenants. It has roiled his political party — one senior member called on Ms. Kim to apologize and compared her to Marie Antoinette. And, polls show, it has become a significant issue ahead of crucial parliamentary elections in an increasingly polarized political atmosphere.

For nearly two years, Ms. Kim has challenged how this deeply patriarchal society views the role of the presidential spouse. Unlike ​past first ladies, who typically remained in the shadow of their husband, she has reveled in media attention and even publicly pushed Mr. Yoon’s government to ban the breeding and butchering of dogs for human consumption. She has talked about Mr. Yoon’s devotion to her, saying in 2022 that he had vowed to cook for her and “kept that promise for the past decade.”

But Ms. Kim has also frequently courted controversy, sometimes in ways that, critics say, highlight her undue influence on the government.

In 2021, when Mr. Yoon, a former prosecutor, was campaigning for the presidency, she apologized for inflating her résumé to promote her art-exhibition business. Then came the release of conversations with a reporter, who secretly recorded Ms. Kim suggesting that she was deeply involved in her husband’s campaign​. She called Mr. Yoon “a fool” who “can’t do anything without me.”​ She also declared that she would retaliate against unfriendly media “if I take power.”