Cho Hyun-ju (Korean: 조현주), also known as Player 120, is a character in both the second and third seasons of South Korean Netflix drama Squid Game. In the series, she is a highly skilled and highly trained ex-Special Forces soldier until she was discharged after coming out as a trans woman, further losing family support and employment. She joins Squid Game to win money in order to support her gender-affirming surgery and possibly move to Thailand to live as a kathoey, and befriends multiple characters, including a woman named Kim Young-mi. She is a leader of her own group with Young-mi and the archenemy of Seon-nyeo. She was created by series creator Hwang Dong-hyuk and portrayed by Park Sung-hoon, a cisgender man. Hwang expressed difficulty in finding a trans female actor in South Korea, citing how South Koreans treat trans people as a reason for casting being difficult. Park worked with trans people in order to portray the character accurately, hoping to avoid caricaturing her.

When it was announced that Hyun-ju would be played by a cisgender man, the show, Hwang, and Park received criticism, with people on social media and critics arguing that casting a cisgender man in this role affirmed an anti-trans notion that trans women are men. It was also argued that it would be more ideal to cast a trans or cisgender woman instead. On release, Hyun-ju was received well for her portrayal and writing, with multiple critics considering the character an authentic representation of trans women. There was also a hope that Hyun-ju would lead to further acceptance and better representation in the future.

Cho Hyun-ju appears in the second season of Squid Game, a trans woman who formerly served as a soldier in the South Korean military as a sergeant until she was discharged for wanting to transition. She also lost family support and struggled to find employment. She was invited to join a game called Squid Game due to the financial strain, as well as her desire to move to Thailand and receive gender-affirming surgery. Her debts would be shown to the rest of the player by a manager, disappointing herself. During the first game, she gets confused as to what Seong Gi-hun is saying. But when a player named Kang Mi-na dies, she along with the other 455 players discover that losing has lethal consequences, proving Gi-hun right. At the end, she assists Gi-hun in rescuing a man who had been shot by No-eul, a North Korean defector and soldier in the Squid Games. During the interim, the surviving players learn that the total reward is 45,600,000,000 won, and they would receive 100 million won per person who died split between the survivors (91,000,000 won). Given the choice to vote to stay or leave, she votes to stay, and the game continues by a slim majority.

Hyun-ju later befriends a woman named Kim Young-mi, who asks to join her, later adding Jang Geum-ja, her son Park Yong-sik, and a shaman named Seon-nyeo, where they have to complete a series of five games while chained side by side. From there, Hyun-ju watches her teammates, as well as stopping Seon-nyeo from disturbing Young-mi and Geum-ja, and slapping her to complete the games or face death. She then tells everyone to look away from her male skills by completing the last game, her team survives. Hyun-ju assists the other members with advice and emotional support. Due to her expenses related to transition and a lack of a source of income, Hyun-ju votes to remain in the game again, with the result being to continue and unintentionally upsets Young-mi. During the next game, Young-mi is killed, causing Hyun-ju to become anguished and blames Lee Myung-gi, but she is then forced to move on. After Mingle, Seon-nyeo mocks Hyun-ju about Young-mi's death and predicts Geum-ja's and Yong-sik's future. Hyun-ju is angered and attempts to attack her, only to be stop and Seon-nyeo walks away. Along with Geum-ja and Yong-sik, she allies with Gi-hun's team, votes to terminate the games, joins the X Team and allies with Park Gyeong-seok, eventually agreeing to participate in a revolt by helping steal guns from soldiers and attempting to take over the facility in order to capture the Masked Officer. After the bathroom fight that results Thanos's death and conflict with the X Team and the O Team, Gi-hun explains a riot that makes the players to kill each other. Hyun-ju hides and pretends to be dead. Once the Masked Officer initiated reinforcements, Hyun-ju strikes back along with the other player. As the soldiers retreated, Hyun-ju joins Gi-hun and some players to help take control the games. She also explains to the players how to reload the guns, revealing to Gyeong-seok that she work in the Korean Special Forces. She provides support while Gi-hun and Jung-bae goes deeper. She sends Kang Dae-ho, an ex-marine and one of Gi-hun's allies, to get more ammo, but when he doesn't return, she goes to see what's wrong, leaving Gyeong-seok and the players to keep fighting against the soldiers. She finds Dae-ho with the ammo, but he is distressed due to the fact he lied about being a marine and is thoroughly unprepared for violence. During this, the others and Jung-bae are killed or apprehended, and the revolt is defeated. She prepares to fight, but Geum-ja stops her which the Masked Officer takes advantage of the revolt.

After Gi-hun awakes and chained by soldiers, Hyun-ju asks about Jung-bae and apologises to Gi-hun, only to be stopped by Yong-sik, who blames Dae-ho for not returning the ammo. Hyun-ju participates in the game Hide and Seek/Keys and Knives as a hider. She is then shocked to see Nam-gyu and the seekers holding hunting knives and the games begin. Hyun-ju and among others, is forced to hide and flee from another team of players attempting to kill them. She teams up with Kim Jun-hee and Geum-ja and assists in delivering Jun-hee's baby, and in the process, defending them by killing two other players (Kim Yeong-sam aka 226 and 202). After finding the exit, she goes back to get them, but is killed by Lee Myung-gi, who then realises she is friends with Jun-hee. Myung-gi closes the door to keep Nam-gyu away from Jun-hee. Geum-ja closes a dead Hyun-ju's eyes. She is put in a coffin after the game ends.

The character of Cho Hyun-ju was developed by Squid Game creator Hwang Dong-hyuk, who compared her in purpose to the character Ali Abdul from the first season of Squid Game. Where he included Ali to represent people in South Korea who are marginalized in non-financial ways, he wanted to include a transgender character to do the same in season 2. He hoped that her choices, actions, and the way she "carries herself in the game" would raise awareness of issues surrounding trans people in South Korea. Hwang intended to cast a trans actor in the role, but found that there were "close to no actors that are openly trans" due to the marginalization of LGBTQ+ people in South Korean society, and expressed displeasure with this. Hwang believed Hyun-ju would be the "most beloved" character of the season.

Hwang ultimately decided to cast actor Park Sung-hoon, a cisgender man. Park believed that he was cast because of a "feminine side" that he developed through growing up with sisters, as well as his performance in the 2021 film Hee-soo. He stated that he approached his performance with "more detail and caution", consulting with trans people to make sure Hyun-ju was not caricaturized. Park avoided exaggerating gestures such as his voice, feeling that altering his naturally deep speaking-tone would "undermine the emotional authenticity". The character's short bangs were chosen by Park, according to him. Describing the character, Park said that Hyun-ju shows "incredible strength, decisiveness, and natural leadership" despite the prejudices she faces, calling her "inspiring" and a character who "breaks down stereotypes". While discussing the fight-choreography for Hyun-ju, stunt-coordinator Park Young-sick explained that, unlike many other characters' fighting which has a "raw survival-action feel", Hyun-ju needed a more "professional feel", taking her "background, profession, and physical [ability] into account".

Hyun-ju is voiced in the Hindi dub by genderfluid performer Sushant Divgikar, and in the English dub by nonbinary transfeminine actor Nicky Endres.