Choi Soon-sil, the friend of former South Korean President Park Geun-hye, has been sentenced to 20 years in prison over corruption.
The 61-year-old was convicted of bribing South Korean conglomerates including Samsung, in a scandal that triggered chaos among the country’s political and business elite.
The Seoul Central District Court also fined Choi $16.6 million.
Choi is the confidante of Park, who was dismissed from the presidency last year after being impeached over a corruption scandal that paralysed her administration and triggered massive street protests. Park denies any wrongdoing.
Prosecutors had demanded a 25-year sentence for Choi, who they said used her relationship with Park for personal gain.
Choi Soon-sil is the prime person of interest in the 2016 South Korean political scandal involving her influence over the 11th President of South Korea, Park Geun-hye.
Choi was accused of using her presidential connections to pressure conglomerates – including electronics giant Samsung and retail group Lotte – for millions of dollars in donations to two non-profit foundations she controlled.
“The guilt of the accused is heavy,” the judge said, adding that she had capitalised on her “long private ties” with Ms Park to solicit bribes and had “meddled in state affairs widely”.
Choi is already serving a three year jail term for a separate charge of corruption, after she was found guilty of using her position to solicit favours for her daughter.
The court has also found Shin Dong-bin, chairman of the Lotte Group, guilty of offering bribes to Choi, and jailed him for two years and six months.
Ms Park was officially ousted in March 2017, following parliament’s decision to impeach her.
She was the country’s first democratically-elected president to be forced from office.
After losing her presidential immunity, she was charged with bribery, abusing state power and leaking state secrets, and her trial began in May.
When the allegations first emerged they prompted numerous mass protests in South Korea, many of which called for Ms Park to step down.
The controversy has fuelled discontent against the government, the political elite and family-run conglomerates which dominate South Korea’s economy.