Heathcliff is the kind of character Anthony Hopkins would play. Indeed, Ralph Fiennes played him in the 1992 version, which doesn't seem like a bad choice to me. Regardless, it would need to be someone who can carry off both a cold cruelty and a flaming anger. While we do see him being rational at times (usually when talking to Nelly, although not always), with nearly everyone he interacts with, Heathcliff treats them like hated possessions. He uses everyone, but seems totally repulsed by them and the fact that he finds them necessary. He gives vent to his anger without hesitation and inspires fear in all around him, especially his own son: "With streaming face and an expression of agony, Linton had thrown his nerveless frame along the ground: he seemed convulsed with exquisite terror.... 'I dread him - I dread him!'"
The violence and intimidation isn't limited to male characters either. On more than one occasion, Heathcliff hits the young Cathy Linton, and hits her hard: "...he seized her with the liberated hand, and, pulling her on his knee, administered with the other a shower of terrific slaps on both sides of the head...." As if that didn't get the point across, Bronte has him call her a 'slut' a few times as well. I'm going to sound like a Victorian when I say this, but I was shocked. The rawness in these moments surprised me and had a decidedly modern feel. Likewise, I never would have imagined a word like 'slut' making it into print in 19th century England. Despite my incredulity, things like this happen over and again in the novel, and seem to be born out of love and madness.
Both motivations are presented in an oblique way, with Heathcliff never making any direct declarations. Truthfully, from a certain point of view, we never even get to see either one born to fruition, and maybe that's the point. Heathcliff's love for the elder Catherine Linton is an obsessive sort of emotion, and the closest he gets to any sort of good will (don't get me started with the names in this book, by the way. The repetition between generations plays an important role in the emotional life of the characters, but makes things hard to understand). He will do anything for her, but I don't think she takes him seriously. It is here more than anywhere else I got frustrated with the narration. The reader has to guess at a lot of the Heathcliff-Catherine relationship, filling in a lot of vague details about why things happen the way they do. The lack of information makes the characters seem capricious and mean. If that was Bronte's intention, she pulled it off masterfully, but I'm not really sure.