The Frost Giants are a race of humanoid giants that live on Jotunheim, one of the Nine Realms. They are ruled by Laufey, king of the Frost Giants, who is also Loki's true biological father.
In 965 A.D., an army of Frost Giants invaded Tønsberg, Norway, attempting to subjugate the earth and plunge it into a new ice age using the Casket of Ancient Winters. However, they were opposed by Odin and an army of Asgardians, who, after a pitched war, drove the Frost Giants back into the heart of Jotunheim and took the Casket, forcing the Frost Giants into a peace agreement.
Centuries later, during Thor’s coronation ceremony, a group of three Frost Giant intruders entered Odin's Vault, attempting to take back the Casket of Ancient Winters, but were dispatched by the Destroyer. Apprehensive of Odin’s lack of concern over the intrusion, Thor convinces Loki, Lady Sif, and The Warriors Three to accompany him to Jotunheim to confront Laufey.
After a divisive battle, the group of Asgardians are saved by Odin, who exchanged a few heated words with Laufey before returning the travelers to Asgard. Odin then banished Thor soon after for his brash actions in this incident, which nearly restarted a war with the Frost Giants.
After Loki learned of his true origins as a Frost Giant, and took control of the throne of Asgard while Odin was in Odinsleep, he made a deal with Laufey to allow him to kill Odin and reclaim the Casket of Ancient Winters, in exchange for peace between Asgard and Jotunheim. However, as part of Loki’s true plot, he double-crossed and killed Laufey and set the Bifrost Bridge to destroy Jotunheim. Despite this, Thor’s timely destruction of the Bifrost ensured Jotunheim and the Frost Giants' continued survival.
After the death of their leader Laufey and Loki's attack on Jotunheim, the Frost Giants were now a broken people. However, when the Bifrost Bridge was destroyed and chaos began to extend over the Nine Realms, they could sense that something had happened. Around 2014, one Frost Giant was a specimen being held in the Collector's Museum on Knowhere before its destruction.