Mephisto!

One of the darkest Marvel characters - Mephiston!
He is not the Devil - but he is very much in league with him!

He tries to bring people down to Hell and to get souls!!
He is an immensly powerful immortal - and overall areally bad guy!!

He has had controntations with superheros - such as The Fantastic Four, The Avengers, Ghostrider! They always manage to get back and avoid drasping Mephistos soul!

But some times the Devil has to work!!