Identify cartoon about a set of fairy/demon twins in a far future where the demon uses propaganda to take over the world

I'm looking for a cartoon from the 70's (I believe) which is about a set of twins; one plump "fairy" and a skeletal "demon". The "fairy" has magic powers and ends up living a life of pleasure, while the "demon" flees and turns evil.

When the "demon" finds his new weapon in the ruins of the ancient world (roughly modern day) he plots to enslave the world; the weapon in question is a set of propaganda movies with Adolf Hitler.