WATCH | Protesters in Seoul demand the president's resignation
For the fourth straight weekend, hundreds of thousands of protesters took to the streets of Seoul and called for the increasingly unpopular President Park Geun-hye to step down.
Who is Park Geun-hye?
Park Geun-hye is South Korea's first female president. When she was elected in February 2013, she pledged to bring "national reconciliation" and greater engagement with North Korea.
Why she's under fire
Last month a Korean television station reported Park was being advised behind-the-scenes by a close friend who does not hold elected office, but has ties to a religious cult.
Choi Soon-sil is accused of using her 40-year friendship with Park to access classified information and solicit millions of dollars in donations to her foundations from the country's major conglomerates, including Samsung.
Why so much fury over Choi in Korea? Imagine if ur head of state had Gypsy palm reader as key aide& let her handle cabinet formation/policy.— Hawon Jung (@allyjung) October 26, 2016
Prosecutors arrested Choi for abuse of power and plan to formally charge her on Sunday.
What's this about a cult?
At the center of this scandal is an obscure religious group called the Church of Eternal Life. According to the Korea Times, Choi's father, Choi-Tae-min, founded the group in the 1970s -- blending Christianity, Buddhism and an indigenous Korean religion.
He considered himself a "modern-day Buddha" and called for his followers to seek eternal life.
There are even talks of me being immersed in a cult or resorting to shamanism ... I would like to say that this is absolutely not true.
South Korea's Rasputin
Because of her alleged influence over Park, Choi Soon-sil has been called South Korea's "Rasputin." Park, however, denies any sort of impropriety.
Not going anywhere
Park has apologized twice on national television, but according to her spokesperson, has no plans to step down before her term ends in 2018.
Her approval rating has taken a major blow since the scandal erupted. The Korea Times reported Tuesday that Park is polling in the single digits.
Prosecutors plan to interview Park next week, making her the first sitting president in South Korea's history to be questioned in a criminal case.