He was 48.

Amid the country's ongoing crackdown on illegal drugs, the actor was under investigation over alleged illegal drug use.

A man in his 40s was found unconscious in a car at a park in central Seoul at 10:30 a.m., and the police later identified him as Lee. In the passenger seat was a charcoal briquette, reported South Korea's Yonhap news agency.

Suicide note found

According to reports, he had left home after writing a memo akin to a suicide note.

"As he was pronounced dead, he wasn't taken to hospital," a fire official told Yonhap.

Lee faced investigation for alleged drug use

Lee has gone through three rounds of police questioning on suspicions of using marijuana and other illegal drugs at the home of a hostess working at a high-end bar in Seoul's Gangnam district on multiple occasions since early this year, the news agency reported.

The actor, however, said he was tricked by the hostess into taking the drugs.

Lee tested negative in both the brief reagent test conducted during police investigations and the lab-based drug test by the National Forensic Service last month, reported Yonhap.

Lee and his movie career

He was best known for his roles in the thriller Helpless (2012), romantic comedy All About My Wife (2012), and crime/black comedy A Hard Day (2014).

He was also known for his role in the Bong Joon-ho's Academy Award–winning black comedy film Parasite, for which he won a Screen Actors Guild Award along with his castmates.

He received several other awards, including a nomination for an International Emmy Award.