After Shao Kahn conquered the realm of Edenia and merged it with Outworld, he decided he would keep the former king's young daughter Kitana alive and raise her as his own daughter. Although Kitana grew up loyal to the emperor, unaware that he had murdered her real father, Kahn feared if she should ever discover the truth about her past, she'd turn against him.
Kahn then ordered his sorcerer Shang Tsung to create an evil, vicious, and loyal clone of Kitana who would take her place. Tsung combined Kitana's essence with a Tarkatan's to achieve this purpose. However, something went wrong with the clone's creation and her face deformed into a hideous Tarkatan's mouth. Rather than disposing of her, she was given the name "Mileena" and introduced as Kitana's twin sister. Instead of replacing Kitana as originally planned, Mileena would be used to watch Kitana and make sure she remained loyal to Kahn.
Kitana and Mileena grew up together as Shao Kahn's personal assassins, even though Mileena secretly harbored a growing bitterness and jealousy towards her "twin" whom Kahn favored over others. Also at some time during her life, Mileena became the secret ally and possible lover of a Tarkatan warrior named Baraka. As Kahn feared, Kitana did finally discover the truth about her past and family. Although she continued to feign loyalty to Shao Kahn, she secretly plotted and waited for the right time to overthrow him.
During Mortal Kombat II, Shao Kahn began to grow suspicious of Kitana and Mileena was ordered to watch over her sister. After finding out Kitana was indeed conspiring with the Earthrealm warriors, Mileena attacked Kitana, but Kitana proved to be the superior fighter and killed her. Mileena's essence descended into Netherealm (Mortal Kombat's hell), giving her even more reason to hate her sister.
Damned to the Netherealm, Mileena found herself recruited by the fallen Elder God Shinnok. During Mortal Kombat Trilogy, she was resurrected by Shinnok and sent to Earth to spy for him during Shao Kahn's invasion. She was also granted the ability to read Kitana's thoughts. After Kahn was defeated, Mileena was summoned back to the Netherealm with Noob Saibot, who was also sent to spy on Shao Kahn.
During Mortal Kombat Gold, Mileena assisted in Shinnok's invasion of Edenia. Seeing this as a chance to finally prove she is superior to Kitana, Mileena allowed her sister to escape Shinnok's dungeons. However, Mileena would again be denied. After Shinnok's defeat, she was again bested by Kitana and secretly locked away in an Edenian prison, perhaps in the hope that she would one day reform.
Mileena remained imprisoned for many years, until the Dragon King, Onaga, returned during Mortal Kombat: Deception and began his own invasion of Edenia. Mileena was freed from her prison by Baraka. She joined Onaga, and was ordered to pose as Kitana in order to mislead the princess' armies while Onaga gathered his strength. Mileena accepted, seeing this as a chance to gain some amount of revenge against Kitana. However, as Mileena began her deception, she also began to consider taking control of the armies for herself.
In Mortal Kombat: Armageddon, Mileena had seized Shao Kahn's fortress using the Edenian forces, all in the 'name of peace'. Though she did this still under the guise of Kitana, she had decided to continue her charade until the Edenian armies were corrupted enough to follow her under her true identity. Though at first confident that Outworld was hers to rule, Mileena soon discovered that Shao Kahn, alongside Goro and Shang Tsung, had mounted an offense against the fortress to re-instate Kahn's rule over Outworld.
At first, Mileena hid in the throne room, and had instructed her mages to cast a defensive spell on the main door. Their magic, however, proved futile against Shao Kahn's brute force, and soon, the former emperor was face to face with Mileena. The mages then stood between the two in a last effort to protect their 'princess', only to be stabbed in the back by her. Revealing her identity to Kahn, Mileena surrenders to him.
Shao Kahn accepts Mileena's surrender, and then commands her to capture Shujinko, who would be used as a bargaining chip in gaining Onaga as an ally. Mileena then sends Shujinko a false invitation, which apparently works, as Shujinko soon finds himself confronted by the dark alliance and quickly imprisoned after being captured by Mileena herself. However, having tasted power for herself, she is no longer content with being a minion. Deciding that she is destined for greater things, and with Outworld out of her reach, sets her sights on ruling Edenia instead.
She appears in Armageddon's Konquest mode, encountering Taven in the dungeons of Shao Kahn's fortress. She battles the intruder, but ultimately is not successful in preventing his progress.
In Mileena's Armageddon ending, she defeats Blaze, causing herself and her "twin" Kitana to psychically fuse together for a moment. When they separate, Mileena finds that she has taken Kitana's features and become beautiful, while Kitana has been cursed with Mileena's Tarkatan teeth. Mileena is now able to take her rightful place as princess of Edenia. She rules in Kitana's place and locks her "sister" in the Edenian palace dungeon, where Kitana eventually goes insane. In Baraka's ending, he chooses Mileena to be his queen after claiming the power of Blaze and murdering his former masters.
, MK:A, MK:2011)
