User blog comment:Tommy,Klaus&Kol2012+/Will Mephistopheles appear on Supernatural?/@comment-3481504-20120710015213/@comment-3481504-20120710024231

No, he's the Devil, and in Ghost Rider, instead of Azazel, Blackheart's his son.

Basic idea: Mephistopheles = Lucifer/the Devil and Blackheart = Azazel.