Sisyphus: The Myth

• Cho Seung-woo as Han Tae-sul
  • Jung Hyeon-jun as young Han Tae-sul

A genius engineer, quantum physicist, CEO and the co-founder of the company Quantum and Time. Rude and arrogant at first, he later becomes more understanding after meeting Seo-hae. He learns of a conspiracy to start a war after he saves the flight he was on from crashing, realising his brother's unexplained death might not have been true after seeing video from the incident.

• Park Shin-hye as Gang Seo-hae
  • Seo Yi-soo as young Gang Seo-hae

A mysterious woman from the future intent on saving the war ravaged world from destruction. She is the daughter of Dong-ki. She has lived in a bunker for eight years before coming out to explore and scavenge war-torn Korea. A battle-hardened elite warrior, she travels to the past to save Tae-sul from death and prevent him from inventing the Uploader, a time machine capable of sending people and things to the past.

• Heo Joon-seok as Han Tae-san
  • Cha Sung-je as young Han Tae-san

Tae-sul's protective older brother who supposedly died. He had faked his death to track down Sigma, whom he has found out to be his younger brother's former classmate, the mastermind behind the future war, and investor in the rise of Tae-sul and Quantum and Time.

• Chae Jong-hyeop as "Sun" / Choi Jae-sun

A former restaurant worker who becomes wealthy with Seo-hae's help. He hopes for romance with Seo-hae but, after being rejected, accepts friendship and treates her like a sister - even calling her "Sis".

• Tae In-ho as Eddie Kim / Kim Seung-bok

Co-CEO of Quantum and Time and Tae-sul's best friend, their friendship drifts apart due to Tae-sul's erratic behavior and Eddie's connection with the financiers taking over Quantum and Time.

• Jung Hye-in as Kim Seo-jin / Kim Agnes

A psychiatrist and daughter of the chairman of Quantum and Time, Kim Han-yong. She previously dated Han Tae-sul before becoming the fiancée of Eddie Kim, though they later break up. Like her father, she is in league with Sigma.

A future version of her, named "Agnes", later appears, running an orphanage for children who crossed over from the future to the past. She is part of the Advance Team.

• Jeon Gook-hwan as Kim Han-yong

The chairman of Quantum and Time and Seo-jin's father, who aids Sigma to cure his wife of ALS.

• Tae Won-seok as Yeo Bong-sun

Tae-sul's loyal assistant and bodyguard. He is left in a vegetative state after the shooting at the Busan Expo, but awakes during the war and learns of Tae-sul's death. He tries to change the future when Seo-hae encounters him on her way to the Uploader.

• Choi Jung-woo as Hwang Hyun-seung

The head of the 7th division of Immigration and Foreign Affairs, also known as the Control Bureau. He is a former NIS agent.

• Yang Joon-mo as Choi Yeon-sik

A high-ranking agent in the 7th division of the Control Bureau.

• Go Yoon as Jung Hyun-gi

A new recruit to the Control Bureau agent and a former cop who is intent on killing Seo-hae, who he is told killed his mother. He is also a colleague of Dong-ki.

• Park Young-bin as Kwon Hyuk-bum

An agent in the 7th division of the Control Bureau.

• Lim Ji-sub as Ma Yong-suk

An agent in the 7th division of the Control Bureau.

• Sung Dong-il as Park Hyeong-do

A man from the future who runs Asia Mart, a convenience store on the outside and a broker business dedicated to helping time-travelers in the inside. He is a member of the Advance Team.

• Jung Ha-joon as Uhm Seon-ho
• Lee Myeong-ro as Uhm Seon-jae
• Lee Si-woo as Lee Ji-eun/Bingbing

Park Hyeong-do's long lost biological daughter from the future. She came to the past ahead of her mother and has been waiting ever since. She wasn't sure to tell Hyeong-do about her true identity, only to be exposed to Hyeong-do by Tae-sul.

• Kim Byung-chul as Sigma / Seo Won-Ju / Seo Gil-Bok[12]

A mysterious character from the future who has been manipulating current events in his favor by using his knowledge of future outcomes. He amasses a fortune very quickly once he has travelled back in time, using published results from the future outcome of horse races, stocks and bonds trading etc., to place bets and options. He was Tae-sul's former classmate in elementary school. He was abused by his father, leading him to kill his father with a chemical formula he learned from Tae-sul when he saved him from bullying. He becomes an amateur painter, known as Seo Gil-Bok. He tries to hang himself because of his miserable life, thinking that no one loves him. Due to his rough childhood and adulthood, he has developed a sense of loneliness and thought that his purpose was to destroy the world. In the future, he is the leader of the Advance Team and the instigator of the nuclear war.

• Lee Jae-won as Kim Dong-hyeon

A fund manager who helps Sigma develop his business in the stock market. At first he is just a stock manager to Seo Won-ju but, after seeing that Won-ju's predictions of the stock market were true, he mimics Won-ju's investments and becomes rich alongside him. He tries to warn Tae-sul about the incoming war, only to be killed. (Ep. 1 & 8)

• Kim Jong-tae as Kang Dong-ki

Seo-hae's father, who teaches her how to survive during the war. He is a veteran Senior Inspector of the National Police Agency and former colleague of Jung Hyun-gi.

• Lee Yeon-soo as Lee Eun-hee

Seo-hae's mother, who sacrifices herself to save her husband and daughter at the beginning of the war.

• Kim Hee-ryeong as Kim Han-yong's wife

A woman with ALS, her husband and daughter are desperate to cure her through any means necessary, even if it means betraying their friends.

• Shin Young-jin as Choi Jae-sun's mother.
• Ha Yu-ri as Choi Go-eun[13]

Choi Jae-sun's sister.

• Kim Byung-chun as a restauranteur

He is the owner of the Chinese restaurant where Jae-sun works, and vows that he would not die of suicide. He is later killed by the Control Bureau, who make it look like suicide and cause Jae-sun to doubt the "official" story.

• Hwang Dong-joo as the co-pilot (Ep. 1–2)

He is the co-pilot of the aircraft Tae-sul was in which crash lands. He is later tortured and killed by the Control Bureau for seeing what he shouldn't have.

• Sung Byoung-sook as Jung Hyun-gi's mother (Ep. 4)

Jung Hyun-gi's mother who originally passes away from illness while Hyun-gi was imprisoned in the Control Bureau jail. Her death was blamed on Seo-hae, giving the present Hyun-gi a reason to join the Control Bureau. Hyun-gi would later return to be with her during her last hours.

In May 2016, screenwriting duo Lee Je-in and Jeon Chan-ho signed a contract with SBS's Studio S to write a 20-episode television series which could not be broadcast on another channel. Studio S provided the writers a workplace where they worked on the script for Sisyphus: The Myth, but the production was eventually cancelled due to the difficulties in casting directors and actors. In December 2018, the duo were put in charge of writing the remaining 36 episodes of Fates & Furies when the previous screenwriter left after writing 4 episodes. However, Studio S did not pay the ₩60 million writing fees which were to be paid within 15 days after the conclusion of the series. The duo terminated their contract with Studio S and turned to JTBC for the broadcast of Sisyphus: The Myth. Studio S filed a lawsuit which they lost in November 2020.[14]

In late September 2019, JTBC confirmed that Cho Seung-woo and Park Shin-hye would star in Jin Hyuk's mystery drama Sisyphus: The Myth.[15]

Principal photography began in May 2020, with Cho Seung-woo joining after completing his work on the second season of Stranger,[16] and filming was completed in early December.[17] Production was temporarily halted in late November 2020 due to the COVID-19 pandemic.[18]