The first indication of Heathcliff's savage personality is found in the opening chapter when the dogs - "A brood of tigers", "fiends" are represented and Heathcliff growls in unison with them. He informs Lockwood that the bitch is not kept for a pet. Catherine's diary provides a clue to the cause of Heathcliff's savagery and hatred, "Poor Heathcliff! Hindley calls him a vagabond, and won't let him sit with us and eat with us anymore... and swears that he will reduce him to his right place". Mr. Earnshaw first describes him thus - "though its as dark almost as if it came from the devil".
Heathcliff's dominant personality quickly becomes evident - "You must exchange horses with me, I don't like mine". This incident demonstrates the extent to which Heathcliff has already been hardened and brutalised. The ragged new-comer to Wuthering Heights is an image of a human creature reduced to its bare animal essence, the naked will to live. Nelly's comments about Heathcliff's ability to withstand pain supports this point of view, "He would withstand Hindley's blows without winking or shedding a tear". Heathcliff's dominant will was being fed by Mr. Earnshaw's favouritism, when he dies this changes, Heathcliff then suffers the tyranny of Hindley. From this point on, the revenge theme begins in the novel. Heathcliff's recollection of the Grange in Chapter 6 is tied this first inkling of revenge, "If I might have the privilege of flinging Joseph off the highest gale and painting the housefront with Hindley's blood".
Heathcliff's language at the Grange, indicated a malevolent attitude, "I've vociferated curses enough to annihilate any fiend in Christendom". Heathcliff's hatred for the Linton family is traceable to this moment - "Yet the villain scowls so plainly in his face, would it not be a kindness to the country to hang him at once before he shows his nature in acts as well as in features". Catherine's stay at the Grange precipitates a further decline in Heathcliff's behaviour. When she returns he is dirtier than before - "I shall be as dirty as I please and I like to be dirty and I will be dirty". Later he confides to Nelly the purpose of his meditations, "I am trying to be settle how I shall pay Hindley back. I don't care how long I wait if I can only do it at last" - "I only wish I new the best way. Let me alone and I'll plan it out, while I'm thinking of that, I don't feel pain". Now the novel's counter-theme to the love story becomes clear - Heathcliff's long premeditated ruthless revenge gradually increasing in scope with all the force of Heathcliff's primitive unchanging will behind it. From this point on, there is in Heathcliff a subordination of all other feelings except revenge.
Now the prince-in-disguise is destined to become a demon, taking on in fact the fiendishness that Nelly had seen lurking in his eyes as a child. Heathcliff's development in this light is traced to Hindley - "His treatment of the latter was enough to make a fiend of a saint". Truly it appeared that Heathcliff was possessed of something diabolical at that stage, he delighted to see Hindley degrading himself past redemption and became daily more noticeable for savage sullenness and ferocity. His disappearance follows his learning of Catherine's engagement - further disappointment - thus widening the scope for revenge.
The returning Heathcliff, despite his outwardly civilised facade, was still demonic in air, "A half civilised ferocity lurked yet in the depressed brows and the eyes full of black fire". In describing Heathcliff to Isabella, Catherine sees him "as a fierce pitiless wolfish man ... and he'd crush you like a sparrow". Catherine marks the change in him, his speech has acquired a new hammerblow rhythm, "What new phase in his character is this", ponders Catherine. She sees beneath his unreclaimed nature something of his diabolism, and she compares Heathcliff to Hindley, "It is as bad as offering Satan a bad soul. Your bliss like his lies in inflicting misery". The marriage to Isabella and his pursuit of ugliness helped to strip the mask of civilisation and releases the central characters in their raw animal states. From here on the plot is dominated by the demonic revenge - from here on Heathcliff strips all others of all the trappings of personality except passion. Sadism now replaces love, and violence is a necessary part if we are to experience this hellish world. In Chapter 14, we see the real Heathcliff and his preoccupation with Catherine leads him into a torrential harangue, "2 words will comprehend my future - death and hell". To Isabella he says, "She degenerates into a mere slut". His talk here is insistent and driven home by a cruel logic. His violent images and use of hyperbole, express an impetuous will, that cannot accept opposition and his rhetoric hardens as it gathers momentum to a language of absolute imperatives, "The nuisance of her presence outweighs the gratification to be derived from tormenting her". His logic depends on a refusal to admit any compromise with passion, any form of mediocrity.
This leads us to the completion of his revenge against Hindley and his becoming master of the Heights. The fight between them is described by Isabella with violent language, Heathcliff is described in demonic terms, "sharp cannibal, teeth, basilisk eyes". Now with victory over Hindley achieved and Edgar retreated in sorrow, the violent aspect of revenge gives way to patience and legalistic guile. To complete his revenge over the Lintons, Heathcliff employs these latter tactics - the marriage between Linton and Catherine is patiently contrived. The question of succession, shrewdly investigated, his guardianship over his son, the decisive cotosill to the inheritance of the Grange. Heathcliff's final thirst for revenge is quenched however by his failure to remain passionate. In the final chapters of the novel, he is torn between two competing passions, that for revenge and that for sympathy and fondness for Hareton. Finally he possesses no ability to prevent the future happiness of the younger generation and deprived of his passion, dies.