system
Given the following post, respond as if you're commenting on Reddit:
human
Do they ever explain why Heimdall was cast out of Asgard?

I enjoyed Thor, but was bothered that they never explained Heimdall's time on earth, when he lived as "Stringer Bell" in Baltimore. This seemed like a major plot detail. Why was he cast out? Who guarded the Bifrost during his absence?  Is this dealt with in the source mythology or comics?
gpt
Oh...you've been hanging out with Amora again, haven't you?

Next she'll have you believing that Heimdall was once pale faced.

Half the things she shows you are insane ravings of a twisted imagination. 

So let's settle things- Heimdall has never been a spaceship captain, a detective, a midgardian criminal, a mercenary or worked in a parchment factory office. 

The most heinous rumor you'll hear is that he's been cavorting with the fiery motorcycle riding spawn of demons. Like the others, it's just not true.

No, Heimdall remains as he's always been, our ever vigilant sentry. Odin would never cast him out, it would be like casting out his remaining good eye.