[quote=@clanjos]
An analogue to Ultraman- a large, benevolent humanoid alien who may have had interaction with humanity in the past.

Edit: The other concept being a Hedorah deal where it’s a creature that feeds on pollutants, but it actively purifies the land/air/water/whathaveyou by its mere presence 
[/quote]

I figured that was where you're going with. That should be fine as well. 

The Anti-Hedorah could also be interesting too.