light following character

Ok, next question I want to make a character carry a torch through a dark scene , and for a ring of light to follow him (as in the pic).

I suspect i need to make an object with a transparent circle on a black background, then somehow set this object to follow the character. I can't do it within the character animation as the 'darkness' needs to appear on top of the foreground layer.

so how can i link an object to a character (only really needs to follow the x-coordinate if that helps) or is there a better way of achieving this effect?

Thanks