Frost is a Lin Kuei warrior and Sub-Zero's apprentice in the Mortal Kombat series, introduced in Mortal Kombat: Deadly Alliance. Having similar cryokinetic powers as her mentor, she is known for her constant attempts to usurp him as the leader of the Lin Kuei.
In Mortal Kombat 11, she is known for becoming a cyborg (in the same vein as Cyrax and Sektor). She later appears as a "Kameo Fighter" in Mortal Kombat 1.
In the original and alternate timelines, the second Sub-Zero became the leader of the ninja clan Lin Kuei and held a tournament to recruit strong members, in which Frost emerges victorious. As she shares similar cryokinetic abilities, Sub-Zero takes her in as his apprentice.
In the original timeline, she accompanies Sub-Zero in aiding Raiden's forces against the "deadly alliance" of sorcerers Quan Chi and Shang Tsung. Unknown to her mentor, Frost had other reasons for traveling with him, as she soon attempts to usurp him as the clan's leader by immobilizing him and stealing his Dragon Medallion (which enhanced his power). Unable to control the Dragon Medallion's power, she was consumed by it, seemingly killing her.
Sub-Zero, forgiving her for her betrayal, searched for a suitable place to lay her body to rest. He encounters the ruins of an ancient structure erected by the ancient race of "Cryomancers", of which he and Frost were revealed to be descendants of, and laid her body in its tombs. Some time later, she awakens and attempts to enact her revenge against Sub-Zero at the Lin Kuei temple. However, her delirium caused her to see Sub-Zero everywhere, causing her to go on a murderous rampage before she is frozen by Sub-Zero. After being revived by Taven, and fighting him due to her delirium, she joins (and dies in) the Battle of Armageddon in an effort to defeat Sub-Zero.
In the timeline with Raiden's changes, Sub-Zero began talks to make peace between the Lin Kuei and their enemy, the revived Shirai Ryu. Angered by this, Frost attempts an assassination against its leader, the resurrected Hanzo Hasashi. Although this has caused a fight between the two leaders, her second attempt was stopped by Sub-Zero and she was banished from the Lin Kuei.
Some time later, the factory powering the Lin Kuei's former Cyber Initiative was restarted by Sektor, brought from a past timeline by Kronika, the Keeper of Time. It is revealed that Frost has undergone the Cyber Initiative procedure and became a cyborg, fighting alongside Sektor and a past-timeline Cyrax in attempting revenge against her former master. After the destruction of the factory, as well as Sektor's detonation, she became the leader of the remaining Cyber Lin Kuei before being disabled by Raiden during the assault on Kronika's Keep.
When returning to the portal to Earthrealm, Frost freezes her master and steals the dragon medallion. Unable to control the medallions power she is consumed by her freezing ability seemingly killing her. Sub-Zero, forgiving her, laid her body to rest at a Cyromancer temple.
The effects of her delirium, seeing Sub-Zero everywhere, caused her to go on a murderous rampage upon arriving at the Lin Kuei temple. Sub-Zero returns to find much of the clan dead, freezing her until she can be cured of her delirium. When she recovers, Frost would have to be tried for her crimes against the Lin Kuei.
(Non-Canonical) After increasing her strength she goes after Sub-Zero again and steals the dragon medallion. With her strengthened powers and new role as the head of the Lin Kuei she travels to Outworld to the Cyromancers temple to implant their souls in the Lin Kuei clan soldiers. Her army of unstoppable Cyromancers conquer the realms leaving nothing but ice remaining.