I was thinking about this iconography of horrorfilms I was talking about. It's actually already there before the Universal horrorfilms, this idea of a charismatic actor playing a monster in unique looking make-up, for example Max Schreck in Murnau's Nosferatu (1922), but I think Universal really used it as a way to present and sell their films: the idea that in a horrorfilm the monster (and thus the actor playing it) is the star as opposed to the actors playing the human parts as with other genres. Of course later on Hammer followed on in this tradition.
However, despite Universal's approach (which was successful), I think in the end it's rather the audience picking out their horror icons. Barker didn't mean for Pinhead to take on the life he did. He wasn't even called Pinhead (he was just called 'lead Cenobite' in the script) and if I remember correctly from the novella, there he spoke in a high, female-like voice. Yet the audience picked him out, nicknamed him and made him an icon (I must say the fact that he is on the poster may have contributed to this too).
But you can't force these icons on the public, hence Mahogany, the Subway Butcher from Midnight Meat Train (played by Vinnie Jones) didn't become an icon.
And this tradition of picking out horror icons exists also among the people who didn't grow up on Universal or Hammer films, so it's something that's inherent to (at least a significant part of) the audience for horrorfilms. Of course merchandise and further sequels, remakes and reboots play into it, but it's really the audience picking them.
The thing seems to be that if a monstrous or villainous character is charismatic in some way the audience will pick him out and make him their kind of twisted hero. The idea seems to be that it's okay to be bad, or to kill, or to do monstrous things, but you have to do it in a charismatic way and you have to have a charismatic personality. If you have that, what would be bad and criminal and objectionable if done by a plain person, suddenly becomes cool. The horror icons represent a kind of perfected and idealized form of the dark side of the human psyche.