These may not seem like the makings of a major scandal. But as Ms. Park nears her last year in office, the revelations have sent her polling numbers to new lows, and a prominent member of her party has called on her to resign from it, while some South Koreans want her impeached.

In part, the accusations have resonated because they feed into longstanding criticism that the president is a disconnected leader who relies only on a trusted few.

But for most South Koreans, the real drama is that Ms. Choi is the daughter of a religious figure whose relationship with Ms. Park had long been the subject of lurid rumors. The figure, Choi Tae-min, was often compared to Rasputin here, and now critics say his daughter is playing the same role.

Mr. Choi was the founder of an obscure sect called the Church of Eternal Life. He befriended Ms. Park, 40 years his junior, soon after her mother was assassinated in 1974. According to a report by the Korean intelligence agency from the 1970s that was published by a South Korean newsmagazine in 2007, Mr. Choi initially approached Ms. Park by telling her that her mother had appeared in his dreams, asking him to help her.

Image Choi Soon-sil, who Ms. Park described as an old friend, in a photo taken from an online news report. Credit... Jeon Heon-Kyun/European Pressphoto Agency

Mr. Choi was a former police officer who had also been a Buddhist monk and a convert to Roman Catholicism. (He also used seven different names and was married six times by the time he died in 1994 at the age of 82.) He became a mentor to Ms. Park, helping her run a pro-government volunteer group called Movement for a New Mind. Ms. Choi became a youth leader in that group.