Sun-kyun, 48, was being investigated for suspected drug use at the time of his death.
A man in his 40s was found in a car in Seoul, South Korea at 10:30 am on Wednesday, according to The Korea Times.
Police later identified the unconscious man as Sun-kyun.
Earlier in the day, police received a report that a suicide note was found after Sun-kyun left his home.
Sun-kyun was being investigated on suspicion of using marijuana and other illegal drugs, the outlet reported.
He was accused of partaking in illegal drugs at the home of a high-end bar hostess multiple times since the beginning of the year.
Sun-kyun claimed that the hostess tricked him into doing the drugs, according to The Korea Times.
The actor tested negative for drugs in two recent tests, according to the outlet.
Before his death, Sun-kyun went through three rounds of police questioning.
The actor was last seen publicly on December 23 while arriving for questioning in the suspected drug use case.
Sun-kyun played Dong Ik in the hit film Parasite, which won the 2020 Oscar for Best Picture.
Parasite became the first foreign language film to ever win the coveted category.
In addition to Parasite, Sun-kyun was known for his work in the 2014 action film A Hard Day and the 2009 drama Paju.
He also starred in 12 episodes of the 2023 crime series Payback, playing the main character Eun Yong.
Tributes have poured in for the famed actor.
“Awful news. Lee Sun-kyun was one of the best actors working in Korean cinema. He was wonderful in Parasite. South Korea has serious problems with suicide. This is unfortunately an all too common story for many celebrities in that country,” one fan wrote.
“I just watched recently him in Payback too. This is too tragic,” another wrote.
“He was amazing in Parasite and Hard Day. This is extremely tragic,” someone else chimed in.
“Lee Sun-kyun was such a great talent in everything I’ve seen him in, but I can’t even think up any tribute because all I can think of is the tragic and heartbreaking circumstances leading up to his death and how this road is such a common story you hear from the industry,” another fan wrote.
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