In the first season, he joined in a secret life-or-death contest consisting of six children's games where he competed with 455 other players for 45.6 billion South Korean won, after incurring significant debts from gambling and unemployment.

Gi-hun was created by series creator Hwang Dong-hyuk and portrayed by Lee Jung-jae, who was cast out of a desire to affect his reputation as a cool actor and show the humanity behind his role.

Seong Gi-hun first appeared in the first season as the protagonist, introduced stealing money from his mother to gamble on horses for a gift for his daughter's birthday.

He discovers his mother in the hospital, unable to get treatment; he attempts to get a loan from his ex-wife, learning she and their daughter are moving to the United States, and he rejoins Squid Game.

During the interim, it is discovered that killing during breaks is permissible, prompting a gangster named Jang Deok-su to go on a massacre with his allies on other players.

After winning thanks to the old man's advice, they barricade themselves for the night, taking shifts keeping watch and dissuading Deoksu from attacking by making him feel paranoid.

He learns that the old man knew he was lying, but let him win anyway, giving his name as Oh Il-nam and thanking him for helping him have fun before his apparent execution.

Some time later, Gi-hun gets his hair styled and colored red, taking Sae-byeok's brother out of an orphanage and bringing him to Sang-woo's mother, including a considerable sum of money.

Gi-hun reappears in the second season, set three years later where he is paying his former loan shark money to hunt down the recruiter, eventually tracking him down.

Gi-hun realizes that the game intends for the players to kill each other, warning his group to hide during this until the soldiers enter so they can steal their guns and take over the facility.

[1] Lee's agency, upon seeing the script for season 1, advised against him taking the role, believing that Gi-hun was "too big of a loser" for him to portray.

He chose to take the role after reading the script for himself, feeling that it was more than just a "typical survival game story" and enjoying the theme of the characters "struggles and emotions.

He described him as "frustratingly stubborn and a selfish figure at decisive moments," and believed that he's an important character, stating that society needed people who could "act on their conscience and do what's right, even when it's challenging."

Teen Vogue writer Jae-ha Kim discussed how the 1997 Asian financial crisis influenced Gi-hun's story progression, particularly the loss of his job and the lack of education denying him opportunities, which she believed led him to taking predatory loans to survive.

[15] Salon writer Melanie McFarland felt that Gi-hun's actions, including draining his mother's bank account for gambling, represented how he, like other characters, fit into roles of either "monetary carnivore or scavenger."

She also stated that Gi-hun's story is a sad one, arguing that he followed the "bootstrapping myth to the letter by working hard and playing by the rules" without anything to show for it.

[16] Authors Yavuz Akyıldız and Elif Şeşen argued that Gi-hun's decision to not use the money and "leads a miserable, depressive, and chaotic life" was a representation of the idea that the game cannot have a winner, stating that the economic structure of society leaves people "lonely and abandoned.

"[17] Screen Rant writer Andrei Sipos felt disappointed by the ending of the first season, believing that Sae-byeok should have survived instead of Gi-hun, feeling that him sacrificing himself for her would have made it more powerful.

He felt that his "actions of atonement" came too late, and that the fact that he abandoned his daughter to go back to the games showed that he was "still the same flawed individual deep down inside."

She argued that Gi-hun, meanwhile, played by the rules and complied with the boundaries of the games, noting the scene where Il-nam and he watched to see if a drunken man in the streets would be rescued or not.

[26] Gi-hun's development in season 2 was well received by Gizmodo writers Germain Lussier and Cheryl Eddy, praising actor Lee Jung-jae for managing to capture his shift into a character with "darker intensity" who is struggling with survivor's guilt.

[23] Collider writer Therese Lacson praised Lee's performance, particularly comparing his character at the beginning of season 2 to the end, and commented that he now filled the same role that Sang-woo had.

[28] Looper writer Akos Peterbencze found Gi-hun's strategy underwhelming, stating that even though he was "far from the smartest character" in the first season, his "cluelessness and naivety" felt unrealistic for someone so dedicated.

[29] Collider writer Ryan Cortero felt that Gi-hun should have gotten a better arc than he did, feeling that his "lack of character development" demonstrated that he was just lucky.

[30] Hankyung writer Kim Ji-won felt that Gi-hun's character in season 2 was not convincing, feeling that his decision to sacrifice people for the greater good made viewers side with the Front Man.