Background Chroma Key

Hey guys,

first of all sorry for my bad english I hope you understand what I want

Is there a function in AE to subtract the background behind an object when I have the background without the object as well? (I want something like a chroma key, just for all without the object)

For example:

I have a video from a game with the character in front. Then I have the same video without the character. Now I want to delete the background so only the character is left on a black background.

I tried all the effects like difference, subtract etc... but they don't work that well.

Is there any effect that can do what I want?

Thanks