Ymir

"You are far from home, Odinson. This is MY domain, and here you will fall..."

- Ymir to Thor

Ymir was the oldest and most powerful of the Frost Giants.

Early Life
Ymir was the leader of the Frost Giants, a race of large creatures that have extensive control over ice. Years ago, Odin managed to steal the Casket of Ancient Winters from Ymir's homeland. Sometime later, wanting the Casket back, Ymir sent hundreds of frost giants to Asgard, in an attempt to regain possession of the Casket. What the giants didn't count on was the intervention of Odin's son Thor. Thor was able to halt the invasion, but could not prevent his friend Lady Sif from being impaled by a frost giant's blade.

Into the Lion's Den
"Hello, Ymir." "You require an answer, Loki. And my answer is yes! I will help you to defeat Asgard."

- Loki and Ymir

Thor was enraged at the frost giants' invasion, and wanted to put an end to their antics immediately. It was then that Loki, Thor's adopted brother, devised a mischievous plan of his own. He told Thor to go to the land of the giants and destroy them if he wished. Thor accepted and journeyed into Ymir's realm. He ventured into the land and fought off hordes of Frost Giants before finally attracting the attention of Ymir. Ymir led Thor into his citadel, where Thor fought off more Frost Giants, and became aware of just how powerful Ymir was. From there, Thor destroyed a large beam which enhanced Ymir's powers over the land. Outraged, Ymir decided to take care of Thor himself, but once again, Ymir had underestimated the god of thunder and was met with defeat.

Mangog Unleashed
At this point, Loki's scheme was working perfectly. After Ymir's defeat, Loki told Thor that he could never truly "defeat" Ymir, as ice can form and reform if Thor breaks him. So Loki told his brother to open up a gateway that would unleash tremendous heat and flame into Ymir's realm, which would of course ensure that the Frost Giants never returned to Asgard. Thor, thinking this to be a brilliant plan, began to open the gateway, only to be stopped seconds later by Ymir, who warned Thor that the gateway would unleash a terrible apocalypse when opened. Thor didn't listen and ended up defeating Ymir again in order to fully open the gateway, which to Thor's dismay happened to be the resting place of Mangog; a large beast with considerable control over flame. When the gateway opened, a beam of fire exploded from out of it, disintegrating Ymir within seconds.

Whether or not Ymir survived the flame is unknown.