I am not going to answer your question completely, but one of the central debates within Wuthering Heights is the nature of Heathcliffe as a character. In particular, there is a dichotomy between descriptions of him presenting him as a monster, and descriptions that suggest he is a man just like one of us.
A few quotes you may wish to use in this regard:
1. Catherine herself urges Nelly to tell Isabella what kind of person Heathcliffe really is: ‘Tell her what Heathcliff is – an unreclaimed creature, without refinement – with out cultivation: and arid wilderness of furze and whinstone… he’s a fierce, pitiless, wolfish man.’
2. Nelly comments on the degradation occurring at Wuthering Heights: "I felt that God had forsaken the stray sheep there to its own wicked wanderings, and an evil beast prowled between it and the fold, waiting his time to spring and destroy."
3. When Heathcliffe bursts in on Catherine and Nelly, he is imbued with almost supernatural strength: "…the casement behind me was banged on the floor by a blow from (Heathcliff), and his black countenance looked blightingly through…His hair and clothes were whitened with snow, and his sharp cannibal teeth, revealed by cold and wrath, gleamed through the dark."
In addition to these specific quotes you may wish to look at the various supernatural adjectives that are applied to the characther of Heathcliffe: "vampire" and "beast" to name but a few.
However, despite these comments on Heathcliffe's monster-like qualities, he is also described as a human.
1. An excellent quote to use is Nelly's reflection on Heathcliffe's misery at Catherine's death: "‘Poor wretch!’ I thought; ‘you have a heart and nerves the same as your brother men!’"
2. Although Lockwood is, undeniably, an unrealiable narrator, he still believes that Heathcliffe is in form at least a gentlemen: "Heathcliff forms a singular contrast to his abode and style of living. He is a dark-skinned gypsy is aspects in dress and manners a gentleman – that is, as much a gentleman as many a country squire…"
Any character study of Heathcliffe needs to investigate this disparity between his human qualities and his monster-qualities.
I will name at least three and provide quotes!
Obsessed: with revenge and Catherine
‘I’ll tell you what I did yesterday! I got the sexton, who was digging Linton’s grave, to remove the earth off her coffin lid, and I opened it. I thought, once, I would have stayed there: when I saw her face again—it is hers yet!—he had hard work to stir me
The moment her regard ceased, I would have torn his heart out, and drunk his blood!
I’ll convince you of the contrary, in a very little while! Meantime, thank you for telling me your sister-in-law’s secret: I swear I’ll make the most of it. And stand you aside!’
Cold-hearted: does not care for anyone besides Catherine
"'You better let the dog alone,' growled Mr. Heathcliff in unison, checking fiercer demonstrations with a punch of his foot"
Mr. Heathcliff never reads; so he took it into his head to destroy my books
Crafty: lies to marry Isabella, and tricks Catherine into getting married to Linton to take the estate.
I should mention that Isabella sent to her brother, some six weeks from her departure, a short note, announcing her marriage with Heathcliff. It appeared dry and cold; but at the bottom was dotted in with pencil an obscure apology
He swore it was not, nor ever should be, mine; and he’d—but I’ll not repeat his language, nor describe his habitual conduct: he is ingenious and unresting in seeking to gain my abhorrence! I sometimes wonder at him with an intensity that deadens my fear: yet, I assure you, a tiger or a venomous serpent could not rouse terror in me equal to that which he wakens.
I do hate him—I am wretched—I have been a fool!