One of the many Norse gods who defends and takes care of Asgard. He is the Keeper of the Bifrost Bridge.
Heimdall was born gifted with senses so acute that they border on the extrasensory. Due to these gifts he was appointed as guardian of Asgard's Bifrost Bridge by Odin.
In the movie Thor, Heimdall serves as the guard of the observatory. He overlooks the nine other worlds for potential threats as well as controls who may and may not enter Asgard through the Bifrost Bridge. He is sworn to be loyal to the king.
Heimdall appears to have a good relationship with Thor. At the beginning of the film, he allows Thor and the others to travel Jotunheim, but warned that if he brought about any threat to Asgard he would not open the path to allow him to return. Later in the film when the Frost Giants invade and freeze him in ice, at the call of Thor to open the gate he uses his strength to break free and allow them him and the others to return before collapsing.