Heimdall

Heimdall has one important duty, to guard Asgard and its gods of Norse Mythology. Heimdall is in charge of defending the Bifrost bridge since his godly powers gives him the ability to see and sense anything within the 9 realms of Asgard, and have such acute hearing that he can hear the grass rising from the ground. This is where Heimdall is normally seen and carries a horn known as Gjallarhorn. If a intruder is approaching his duty is to blow this horn where its sound travels to the corners of space warning the gods. He's also seen in the movie "Thor".