Heimdall

Heimdall is the guardian of Asgard, he guards the Bifrost bridge. He blows his horn when Ragnarok comes. He's also an Aesir. Heimdall can see and hear across time.

Marvel's Heimdall
In Marvel, Heimdall has quite a big role. He's Sif's brother, which was real in Norse Mythology, and he weilds a sword capable of sending waves of energy called the Uru blade. His horn is called Gjallarhorn. When other gods visit other realms, they have to call Heimdall's name and Heimdall will send them back to Asgard.

Families and Relations
Sister: Sif

Mother: The Nine Mothers of Heimdallr