Which Iron Man Are Black Sabbath Singing About?

Joshua @ Braniac wonders which Iron Man the Black Sabbath song is about. the Marvel Iron Man, or the Ted Hughes Iron Man and comes down on the Ted Hughes side.

I'd just always assumed that was the case. Urban metal knowledge. Would four Brummie lads in 1970 have easy access to Marvel comics? Maybe it's just me, but I've never really heard much about Iron Man, isn't he just some minor Marvel character? Is it a UK / US thing? Or is it because I'm ignorant of Marvel comics? I think the upcoming movie will probably pass me by.