It was The Devil/Satan in the beginning way back in Marvel Spotlight 5, circa issue 75 or 76 of Blaze's first GR series it was then Mephisto.
It was never Hellstrom's dad.
Years later after the Dan Ketch GR was retired, Blaze was brought back and then it was changed back to the Devil.
Aaron's run established that the Riders are a force from heaven created by the Almighty.
Dan Ketch GR: allegedly Noble Kale, allegedly an ancestor of Dan Ketch and Johnny Blaze as they were revealed to be brothers. Note: the revelation that they were brothers came from Caretaker whose ability to be truthful was dubious at times. However after his series ended with issue 93, Spider-Man 93 (I think was the number) came out and Mackie reset the Rider back to default as it were (which was good as Ivan Valez jr screwed up the book) and cast doubt upon the Noble kale thing.
Dan gets repowered in the Blaze series that brought on the heaven revelation and was still powered at the end but apparently was depowered again.
All too confusing. Let's hope the new series (featuring Johnny, Danny AND Mephisto(y) will at least pick one and stick to it.