Psychopath Diary

Psychopath Diary is a 2019 South Korean television series starring Yoon Shi-yoon, Jung In-sun and Park Sung-hoon. It aired on tvN from November 20, 2019 to January 9, 2020.

Synopsis
Yook Dong-sik (Yoon Shi-yoon), an analyst who works at Daehan Securities, has a timid personality. He can't even get angry at the people who look down upon him. One day, shortly after failing on his attempt of suicide, he witnesses a murder. He unintentionally picks up a diary belonging to the murderer, on which was written the log of his murders. He flees with the diary, but he is accidentally hit by Police Officer Shim Bo-kyung's (Jung In-sun) patrol car which causes him to suffer from retrograde amnesia. Due to the diary in his possession, Dong-sik mistakenly believes he is a psychopath. Since that moment, his behavior started to change. Bo-kyung, who got involved with Dong-sik, decides to catch the serial killer.

Meanwhile, Seo In-woo (Park Sung-hoon), the director and son of the chairman of Daehan Securities where Dong-sik works, turns out to be the heartless psychopath serial killer. He loses his diary when his 6th victim, a homeless old man tossed his diary away. He feels insecure ever since, He is obsessed and in love with DongSik.

Main

 * Yoon Shi-yoon as Yook Dong-sik, a timid and pushover man who works as a clerk at Daehan Securities. His weak personality begins to change when he perceives himself as a killer.
 * Jung In-sun as Shim Bo-kyung, an officer in a patrol station.
 * Park Sung-hoon as Seo In-woo, the real psychopathic serial killer who is also the director of Daehan Securities where Dong-sik works at.

People around Yook Dong-sik

 * Lee Han-wi as Yook Jong-chul, Dong-sik's father.
 * Hwang Geum-byul as Yook Ji-yeon, Dong-sik's older sister.
 * Kim Gyul as Jo Yong-gu, Dong-sik's brother-in-law.
 * Jung Su-bin as Yook Dong-chan, Dong-sik's younger half-brother.
 * So Hee-jung as Na In-hye, Dong-sik's step-mother, Dong-chan's mother.
 * Heo Sung-tae as Jang Chil-sung, a gangster who lives at Unit 708. He later addresses Dong-sik as his 'Big Boss' after mistakenly believes him to be a serial killer.

People around Shim Bo-kyung

 * Choi Sung-won as Heo Taek-soo, Bo-kyung's partner.
 * Kim Myung-soo as Shim Seok-gu, Bo-kyung's father who is a former investigator police.
 * Lee Kan-hee as Lee Suk-yeon, Bo-kyung's mother.
 * Lee Hae-young as Officer Ryu Jae-joon

People around Seo In-woo

 * Park Jung-hak as Seo Chung-hyeon, In-woo's father who is the chairman of Daehan Securities.
 * Yoo Bi as Seo Ji-hun, In-woo's step-brother and managing director of Daehan Securities.
 * Yoon Ye-hee as Kim Eun-shil, Chung-hyeon's wife and Ji-hun's mother.
 * Kim Hye-na as Seo Ji-eun, In-woo's step-sister.
 * Lim Il-gyu as Kim Chan-il, In-woo's brother-in-law.
 * Han Soo-hyun as Kim Mu-seok, former detective who now works for In-woo.

People at Daehan Securities

 * Choi Dae-chul as Gong Chan-seok, the manager of Team 3 and Dong-sik's boss who is selfish and rude.
 * Kim Ki-doo as Park Jae-ho, Dong-shik's cunning team member who claims to be his best friend.
 * Jo Shi-nae as Han Jung-ah, Dong-sik's colleague.
 * Lee Min-ji as Oh Min-joo
 * Choi Tae-hwan as Shin Seok-hyun
 * Hwang Sun-hee as Jo Yoo-jin

Others

 * Gu Ja-geon as a bully

Special appearances

 * Jung Hae-kyun as Kim Myung-gook, a homeless man. (Ep. 1–2)
 * Yura as a girl with a dog in park (Ep. 2)
 * Nam Jung-hee as murder victim (Ep. 2)
 * Jo Yoon Ho as Chil-sung's junior (Ep. 2)
 * Han Ji-eun as a woman with a big guy (Ep. 2)
 * Yoon Ji-on as Joo Young-min (Ep. 4–5)
 * Lee Hyun-woong as Oh Myung-dal (Ep. 12–13, 16)

Production
The first script reading was held in August 2019 in Sangam-dong, Seoul.