Heimdall was the all-seeing and all-hearing Asgardian and former guard of Asgard's Bifrost Bridge. He could see and hear nearly everything that happens in the Nine Realms. Despite vowing to obey the orders of Odin, Heimdall was prepared to commit treason if it meant protecting the Realms, as he allowed the Warriors Three to return Thor from Midgard to defeat Loki.
When Asgard was attacked by the Dark Elves, Heimdall discoveredhis powers were blocked by the Elves so he was forced to onceagain commit treason to help Thor destroy Malekith and protect theNine Realms. Under Loki's disguised regime over Asgard, Heimdallwas banished from his position.
