This is an interesting god conceptually. He is the watchman of the gods in Norse mythology, and he serves as the keeper of the Bifrost (rainbow bridge) at the entrance to Asgard.
Here is a somewhat older rendering from Marvel Comics …
… and a more recent one.
I have lauded the Disney Marvel universe in my series, The Modern Pantheon (see black strip at left), and I mentioned then that I am intrigued to see how they develop his character further (perhaps in Thor: Ragnarok?). He is interpreted interestingly by Idris Elba, as can be seen in Thor, Thor: The Dark World, and (briefly) Avengers: Age of Ultron.
So I did something I hadn’t done in a long time. I bought some graphic novels. And what did I choose? I decided to read Thanos: The Infinity Revelation and Thanos: The Infinity Relativity, both by Jim Starlin, Andy Smith, and Frank D’Armata. This betrayed my interest in a character which I had seen during those brief clips at the end of The Avengers and Avengers: Age Of Ultron (both directed by Joss Whedon) as well as more prominently in Guardians Of The Galaxy (directed by James Gunn).
We know from his appearances so far that Thanos is a very powerful being who is attempting to collect the Infinity Stones for some nefarious purpose, so he’s not a very nice guy. I mean, he ordered an invasion of earth, for crying out loud. The movies have not yet developed his character sufficiently, but if they incorporate any of his characteristics from the comics, he should be interesting and fun to watch. In the comics, he is an intellectually as well as physically advanced alien with a nihilistic intellect. He loves death (literally), and death ultimately has no power over him. He is possessed by intellectual curiosity and cannot resist a good puzzle. This sense of inquiry could make him a psychological study to rival Loki if he is written properly. I look forward to seeing him in the Infinity Wars adaptations scheduled for future release.
I must confess to knowing very little about this character due to his mainly supporting role in the movies in which he has appeared. Although he can be seen in Thor, Thor: The Dark World, and Avengers: Age of Ultron, Heimdall to me is primarily an image, but I like this character for what I don’t know about him precisely because he allows my imagination to run freely. It’s not what he is as much as what he triggers by association. I’m sure that Idris Elba, the actor who portrays him, has much to do with this. His screen persona gives an impression of height armored and helmeted in gold, while the depth of his voice underscores the fierceness and loyalty of his character.
Heimdall is the guardian of the Bifrost (rainbow bridge) which serves as the teleportation system of Asgard. His eyes miss nothing – well, almost nothing. Loki did manage to slip some intruders past him once, and Thor’s likable but villainous brother also found a type of “back door” in and out of the kingdom. Still, how many of us can claim that we’ve only made two mistakes?
Having worked under educational administrators who can be rather hidebound about rules (much less so their intelligent interpretation), I appreciate that the keeper of the bridge recognizes when it is necessary to break the letter of the law in order to serve its spirit. I understand that he will be seen again in Thor: Ragnarok, and I look forward to seeing how this potentially interesting character will be further developed.