The scandal, which has generated huge protests, revolves around Ms Park's relationship with an old friend, and has brought allegations of cult activities, influence-peddling and leaks of classified information. Ms Park, but has now said it is up to parliament to decide if her term should end early.
Few claims have been off-limits in the media coverage of the scandal, with some reports going as far as suggesting the president is a puppet who hosted shamanist rituals at the presidential compound. But many of the lurid claims are unsubstantiated. The official investigation focuses on Ms Choi's alleged abuse of her closeness to the president to enrich herself and influence policy, as well as her handling of classified documents.
Park Geun-hye and has said she is prepared to stand down, amid an escalating corruption scandal. Three opposition parties introduced a bill on December 03 to impeach Park, who is accused of abuse of power, putting her in danger of becoming the first democratically elected South Korean leader to leave office early. The heads of nine conglomerates, or chaebol, including Samsung Group's de facto leader Jay Y. Lee and Hyundai Motor Group Chairman Chung Mong-koo, are scheduled to appear at the inquiry.
President Park is alleged to have been personally involved, instructing Ms Choi and two presidential aides to collect money for the launch of Ms Choi's foundations, according to prosecution documents submitted to the court. Ms Choi is also accused of having received large numbers of confidential government documents from Ms Park, via an aide. These allegedly included information about ministerial candidates and North Korea.
Ms Choi is also alleged to have used her presidential connections to pressure companies for millions of dollars in donations to two non-profit foundations she controlled. The claims have even swept up Samsung in the investigation. There are even claims Ms Choi took advantage of the president's wardrobe budget - buying cheap outfits and keeping the change.
On Sunday 20 November, Ms Choi was formally charged with various offences, including abuse of authority, coercion, attempted coercion and attempted fraud. Two former presidential advisers were also charged by prosecutors, who said they thought the president conspired in the wrongdoing.
The allegations are strenuously denied by Ms Park. When she was first questioned in October, Ms Choi said she had committed an "unpardonable crime", though her lawyer said this was not a legal admission of guilt.
Witnesses have claimed that Ms Choi received briefings and official papers long after that occurred. Documents were also discovered on an unsecured tablet computer found in an old office of Ms Choi's. But the tone of the president's pronouncements has changed over time. She began with opaque apologies: "Regardless of what the reason may be, I am sorry that the scandal has caused national concern and I humbly apologize to the people."
Park has herself admitted some lapses. She says she did consult Ms Choi for advice, and that she helped her edit her speeches, but that this stopped once she had a team of advisers in place. Some days ago, she offered to step down and asked parliament to decide how and when she should leave office. Opposition parties rejected the proposal, calling it a ploy to buy time and avoid being impeached, and vowed to push ahead with impeachment.
The leader has apologized three times over the affair, which started when CNN South Korean affiliate JTBC found evidence that Park confidante Choi Soon-sil had received secret documents on an abandoned tablet device. Choi, who does not hold an official government position, is accused of using her relationship with Park to accumulate millions of dollars in donations to her foundations. Choi is charged with abuse of power, fraud and coercion, and two of Park's former aides also face criminal charges.
Prosecutors have said they want to speak to Park after naming her as a suspect in the corruption probe. Her attorneys have said she is willing to cooperate, but she said this week she was too busy to meet with prosecutors.
On Saturday, tens of thousands of protesters again took to the streets of Seoul to push for Park's ouster. A candlelight protest held on the main boulevard facing the presidential offices and residence -- known as the Blue House -- follows weekly mass demonstrations in the capital and other cities since late October.
The impeachment vote is set for Friday. If successful, it would require the approval of South Korea's Constitutional Court, a process that experts said would take at least two months. The opposition parties need at least 28 members from Park's Saenuri Party to secure the two-thirds majority required for the bill to pass. At least 29 of them are believed to be planning to vote for the bill, members of the breakaway faction said. Parliamentary Leader of the main opposition Democratic Party, Woo Sang-ho said, "The chances of the impeachment bill passing on December 9 are 50-50.''
Park's presidential Blue House aides addressed a parliamentary hearing over the allegation that Park and her friend, Choi Soon-sil, as well as a senior aide to Park, put pressure on conglomerates to pay money to foundations that were set up to promote Park's policy initiatives. They are expected to be questioned about how they came under pressure from Park and whether they were promised favors in return. Park has denied wrongdoing but has apologized for exercising poor judgment.
The large protest rally on Saturday, which organizers said was the largest yet with 1.7 million participants and followed Park's third apology last week, as the clearest reason why she should be ousted. Police said the crowd in Seoul reached 320,000 at its peak.
South Korea's opposition parties said they would vote on a motion to impeach Park. With the impeachment vote looming, breakaway members of the ruling Saenuri Party are instead pushing for Park to announce a timeline to resign, arguing that impeachment then would be unnecessary.,
The nonloyalist members of the Saenuri Party members have vowed that if Park does not confirm her resignation date by that deadline they will vote for impeachment two days later. The three opposition parties have a combined total of 165 out of the 300 legislative seats. A two-thirds majority of 200 votes is required to pass the impeachment motion, so members of Park's party will be needed to help pass it.
If successful, the motion would then pass to the constitutional court for consideration. Justices have 180 days to decide the case after it is referred to them. In a nationally televised speech last month, Park said she deeply regretted her actions. "I again deeply apologize for causing an immeasurable disappointment and worry," she said. "All this is my fault, caused by my negligence." However, since the corruption scandal broke, a survey by Gallup Korea showed Park's approval ratings dipped into single digits, making her one of South Korea's least popular leaders since the country became a democracy in the 1980s.
Embattled President Park Geun-hye faces an ultimatum from her own party: Announce a timeline for her resignation or face possible impeachment. Corruption scandal paralyzes presidency.
Park does not face the threat of charges because the South Korean Constitution gives immunity to the sitting President.
Park, who's been dogged by a classified information scandal involving a longtime friend, said earlier this week she would resign if that's what the National Assembly wants.
Many observers see stepping down as a way for Park to avoid the embarrassment of impeachment as opposition parties look to press ahead next week with a vote to unseat her.
Park stopped short of specifying a date for her resignation, leading some breakaway members of her Saenuri Party to ask her to set a timeline for her departure. Mainstream members of her party have stipulated that she must stand down. Her five-year term is set to end in February 2018.