Yoo Hae-jin on 30 Years in Film, Park Hae-il and Lee Min-ho in 'The Assassins'

Veteran South Korean actor Yoo Hae-jin grew quiet for a moment during a recent interview. The subject was his win at this year's Baeksang Arts Awards, one of South Korea's top entertainment honors, and the reaction from the people around him.

"When I won at Baeksang, I was so grateful that others were happy for me," he said. "I think people share that joy because we've spent a long time together. Maybe they were thinking, 'Knowing his past, this couldn't have been easy.'"

Yoo, who started with bit parts before moving to supporting roles and eventually leading ones, is now in his 30th year in the industry. The congratulations, he said, hit differently after all that time.

Now he is back with a new film. "The Assassins" (Amsaljadeul), directed by Heo Jin-ho, opens in theaters on Sept. 23. The film is based on the Aug. 15, 1974 shooting of South Korea's first lady, and follows the people digging into who was behind it and what really happened. Yoo plays Cheol-gu, a police officer who was at the scene that day.

"It will be a chance to think about the questions that still remain," he said. "Who was behind it, what the truth was."

Yoo has a reputation for slipping easily into period pieces. Asked for his secret, he laughed and pointed to his face.

"It's very simple. It's my looks. Honestly, I think it helps a lot. Costume and makeup aren't a big worry. Haha."

Park Hae-il plays Jae-hwan, a senior social affairs reporter, and shares much of the film with Yoo. Yoo praised his co-star's focus on set.

"His eyes never miss anything, and I really like that," he said. "It's one of the things I envy because I don't have it myself."

Lee Min-ho plays Young-il, Jae-hwan's junior reporter, who also witnesses a shocking moment at the scene. Yoo said Lee brought strong energy to the shoot.

"His eyes are sharp, and he's really smart," he said.

Talking about both actors, Yoo softened.

"Park Hae-il is a very serious person. There used to be something a little stiff about him, but now that's what makes him funny. It actually makes him feel closer. Lee Min-ho feels like a very handsome younger brother. Maybe I shouldn't call him a brother. Haha. Anyway, he's a good friend. It's nice when he reaches out."

Yoo has had a good first half of the year. "The King's Warden" (Wanggwa Saneun Namja), directed by Jang Hang-jun, opened in February and became a hit.

"We were out doing promotion when we passed 1 million viewers," he said. "On the bus, we were so happy that we took a commemorative photo like we'd hit 10 million."

The team from that film has been cheering on his new one too. Yoo said he ran into Jang at the Jecheon film festival.

"He watched the trailer and told me, 'Hae-jin-ah, I think this is going to do well. If there's anything I can do to help with promotion, just say the word,'" Yoo said, laughing.

Jang and his wife, screenwriter Kim Eun-hee, are expected at the VIP screening, along with Park Jihoon, who plays King Danjong in the film, and Kim Min, who plays his son.

The new film is built around a real event, but Yoo said he did not feel any additional pressure because of that. Asked what kind of responsibility he felt as an actor while shooting "Assassins," he kept it plain.

"It's the same with any project," he said. "I looked at it as one piece of work and approached it through the character."

He described the appeal of the film in terms of its people.

"I think the strength of this film is the density of its characters. Chasing the shape of the truth inside a shocking event felt like solving a Rubik's cube. Getting closer to who was really behind it, that part was fun."

Even after three decades in film, Yoo is not letting his guard down. He said he wanted to tell himself that he has done well so far.

"I want to say, 'good job,'" he said. "But it also made me think I need to be more careful and work hard on the next one."