A powerful but peaceful leader, Odin is the Allfather of all Asgard who is dedicated to perserving peace between the Nine Realms of Yggdrasil.
When the Frost Giants invaded Earth in medieval times, a young Odin led Asgard to war, eventually driving the Giants back to their realm of Jotunheim. Odin stole from them the Casket of Ancient Winters, the source of power. However, unbeknown to all but Frigga, Odin also took the son of Laufey, leader of the Frost Giants. This cost Odin his right eye, which he later covered with an eye patch. The adoptive son was named Loki. This victory led to a new era of peace and stability, which Thor shattered by invading Jotunheim. Odin then exiled his son to earth.
Loki went on to become the main antagonist of the Thor movie. When Odin had a heart attack during Thor, he was put into stasis, or Odinsleep, in hope of recovery. Odin awoke right at the climax of the movie, saving both his sons from a long fall into darkness. However, Loki let go of Odin's hand and fell, while Thor was saved.