Understanding South Korea's corruption and bribery scandal

South Korea's President Park Geun-hye has become the country's first democratically elected leader to be forced from office.

That dubious honour was imposed on her yesterday, when judges unanimously upheld the parliament's decision in December to impeach her over a corruption scandal.

That scandal, which has generated huge protests, centres on her relationship with an old friend, and has brought allegations of cult activities, influence-peddling and leaks of classified information.

What is the relationship at the heart of the scandal?

In 1974, Park Geun-hye's mother was killed by a North Korean spy who had intended to kill Ms Park's father, then-military leader Park Chung-hee. Ms Park, then aged 22, became a stand-in first lady for her widowed father.

It was then she got to know Choi Tae-min, a pseudo-Christian leader who set up a cult called The Church of Eternal Life. He said he had been visited by the soul of Ms Park's late mother who asked him to guide her.

He became Ms Park's mentor, while also amassing considerable wealth and power.

When President Park senior was assassinated by his head of intelligence in 1979, there was speculation it was because the spy chief was worried the president was being manipulated by the man dubbed "the Korean Rasputin".

By this point Ms Park was firm friends with Mr Choi's daughter, Choi Soon-sil. Their critics believe Ms Choi perpetuated her father's habits.

Timeline

• 2012: Ms Park wins her party's primary to become presidential candidate and defeats liberal candidate Moon Jae-in.
• 25 Feb, 2013: Ms Park is sworn in as the first female president of South Korea.
• 25 Oct, 2016: Ms Park makes her first public apology for giving Ms Choi access to draft speeches during the first months of her presidency.
• 31 Oct, 2016: State prosecutors arrest Ms Choi on suspicion of exerting inappropriate influence over state affairs.
• 4 Nov, 2016: Ms Park makes her second televised apology, saying she would take responsibility if found guilty.
• 20 Nov, 2016: Prosecutors indict Ms Choi on charges of abuse of power and attempted fraud.
• 29 Nov, 2016: In her third televised apology, Ms Park asks Parliament to decide how and when she can give up power over the scandal.
• 9 Dec, 2016: Parliament votes to impeach Ms Park. She is stripped of powers while awaiting a court decision on the vote. Prime Minister Hwang Kyo-ahn becomes acting president.
• 1 Jan, 2017: Ms Park denies wrongdoing, calling accusations "fabrication and falsehood".
• 6 March: The special prosecutor says Ms Park colluded with Ms Choi to take bribes from the Samsung Group, paving the way for her to be prosecuted if she is ousted from office.
• 9 March: Samsung heir Lee Jae-yong's trial begins on charges of bribery and embezzlement. He is indicted on charges including pledging $US37.24 million in payments to Ms Choi.
• 10 March: Constitutional Court upholds Parliament's vote to impeach Ms Park, removing her from office.

Why has the friendship become problematic?

On 20 November, Ms Choi was charged with various offences, including abuse of authority, coercion, attempted coercion and attempted fraud. She is now on trial.

Few claims have been off-limits in the media coverage, 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.

Ms Choi is accused of using 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 - the firm is one of eight that has admitted making payments to the foundation, but denies it did so in return for any favours.

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.

There are even claims Ms Choi took advantage of the president's wardrobe budget - buying cheap outfits and keeping the change.

What do the two women say?

They have both apologised, but it remains unclear exactly what for.

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.

President 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.

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 apologise to the people."

But she has moved on to "heartbroken" public confessions of naivety: "Sad thoughts trouble my sleep at night. I realise that whatever I do, it will be difficult to mend the hearts of the people, and then I feel a sense of shame."

She had said she was willing to be questioned by investigators, but has so far resisted their attempts to speak to her.

Her spokesman said the prosecutors' allegation that she colluded with Ms Choi was "deeply regrettable" and "but a house of cards built on repeated imagination".

So how is Samsung involved?

Samsung's de facto head, Lee Jae-Yong, is now on trial on a string of corruption charges, including bribery and embezzlement.

Prosecutors allege Mr Lee, heir to South Korea's largest conglomerate, approved payments of 41bn won ($36m, £29m) to Ms Choi's foundations, to win government support for a big restructuring of Samsung.

He denies the allegations, as do four other Samsung executives facing trial.

Lee Jae-yong: Samsung's heir apparent

• Grandson of Samsung founder Lee Byung-chul, son of current chairman Lee Kun-hee.
• Also known as Jay Y Lee, the 48-year-old has spent his entire career in the company.
• Is vice chairman of Samsung Electronics and was nominated to join the firm's board in October 2016.
• Despite his arrest, still widely expected to take overall control of Samsung.
• Critics say his rise through Samsung has been due to his birth, not his business experience.

Mr Lee, also known as Jay Y Lee, is currently vice-chairman of Samsung Electronics. But since his father, Lee Kun-hee, suffered a heart attack in 2014, he is considered de facto boss of the entire Samsung Group conglomerate.

In a December parliamentary hearing, Samsung admitted giving a total of 20.4bn won to two foundations, but denied seeking favours.

Mr Lee also confirmed the firm gave a horse and money to help the equestrian career of Ms Choi's daughter, Chung Yoo-ra, something he said he regretted.

Investigators are assessing whether the payments bought support for a controversial merger of two Samsung affiliates.

Some investors opposed the deal, saying one of the affiliates's shares were undervalued, but support from a major shareholder, the state-run National Pension Service (NPS), helped the deal go through.

The official who oversaw the NPS has since been charged with putting pressure on managers to approve the merger, which strengthened Mr Lee's control over a key part of the conglomerate.

Is anyone else involved?

Several former presidential aides have been investigated.

An Chong-bum, Ms Park's former senior secretary for policy co-ordination, has been charged with abuse of authority, coercion and attempted coercion, and Jung Ho-sung is accused of passing classified presidential documents to Ms Choi.

Local media have also been busy finding colourful associates of Ms Choi who were close to the president, including various celebrities and her personal trainer, who was appointed as a presidential aide.

What now?

The impeachment verdict against Ms Park stripped her of presidential immunity. She could now face criminal charges.

The constitutional court's ruling, while not a criminal trial, will not have given her much hope she will avoid that.

It ruled she broke the law by allowing Ms Choi to meddle in state affairs, and breached guidelines on official secrets in leaking numerous documents.

She must now leave office and new elections must be held within 60 days.

- BBC