Though he was brought home by Mr. Earnshaw following a journey to Liverpool, there is no definitive answer to his ethnicity. Liverpool by 1740 had surpassed Bristol and London as the slave-trading capital of Britain. Did Emily Brontё envisage him to be a black man by mentioning Liverpool? Nelly once said to Heathcliff: “If you were a regular black …”. He was also described as a “dark-skinned gypsy”, or “a little Lascar”, and dark haired, with a “half-civilized ferocity” that “lurked yet in the depressed brows and eyes full of black fire”, and with dusky skin. Were these references merely meant to imply foreignness, otherness, and, frankly, danger and nothing to imply race? What was his ethnicity?
TL;DR: Heathcliff’s ethnicity is ambiguous. To the other characters, his appearance strikes them as foreign, but they cannot say with any certainty where he appears to be from. Mr Earnshaw’s unsatisfactory account of Heathcliff’s origins, together with his preference for the boy, lead us to suspect that Heathcliff may be his illegitimate mixed-race son.
Lockwood says that Heathcliff is “a dark skinned gypsy, in aspect” (chapter I). Several other characters also call him a “gipsy”: Mrs Earnshaw (IV), Hindley (IV), Mrs Linton (VI), Joseph (IX), and Edgar (X).
Nelly describes him as a “black-haired child” (IV) with “dark face and hair” (X) or “black hair, and eyes” (XX) and likens his eyes to a “couple of black fiends” (VII). She advises him, “A good heart will help you to a bonny face, my lad, if you were a regular black” (the implication being that he is not one) and says playfully, “You’re fit for a prince in disguise. Who knows but your father was Emperor of China, and your mother an Indian queen” (VII). When he returns after making his fortune, “the cheeks were sallow, and half covered with black whiskers” (X). When he is ill, she is disturbed by “Those deep black eyes! That smile, and ghastly paleness!” (XXXIV). After he dies, she “combed his black long hair from his forehead” (XXXIV).
Mr Linton says he is “a little Lascar, or an American or Spanish castaway” (VI). (A lascar is a sailor from south or south-east Asia. The implication, I think, of “castaway”, is that his complexion is dark as if sun-tanned.)
Isabella says that when Heathcliff prayed, “God was curiously confounded with his own black father” (XVII).
I don’t think we can take any of the racial epithets literally: none of the characters have certain knowledge of Heathcliff’s background, so all that they can be saying is that he seems foreign in appearance.
Mr Earnshaw’s story about how he found Heathcliff is given as follows by Nelly:
The master tried to explain the matter; but he was really half dead with fatigue, and all that I could make out, amongst her scolding, was a tale of his seeing it starving, and houseless, and as good as dumb, in the streets of Liverpool, where he picked it up and inquired for its owner. Not a soul knew to whom it belonged, he said; and his money and time being both limited, he thought it better to take it home with him at once, than run into vain expenses there: because he was determined he would not leave it as he found it. (Chapter IV)
But is this a credible explanation? A couple of aspects of the episode are suspicious. First, why did he choose to walk all the way to Liverpool and back—“sixty miles each way, that is a long spell!” (IV)—when he could have ridden? We know that Mr Earnshaw owned horses, since Cathy can ride—“she was hardly six years old, but she could ride any horse in the stable” (IV). Perhaps he walked in order to be incognito—if he had ridden, he would have had to stable his horse at his destination, where he might be recognized. Second, what was his business in Liverpool? It must have been of short duration, since he was back in only three days, and it is hard to imagine that walking a hundred and twenty miles (half of it carrying the child) in that time left much spare for errands. But whatever his business was, it was urgent enough to leave the harvest in the hands of others.
So I think a plausible idea is that Mr Earnshaw was summoned to Liverpool specifically to collect Heathcliff, but he was unwilling to admit this to his family, preferring to tell the foundling story instead. Why was he unwilling? William Empson considered the following possibility:
It seems clear what Emily would have added to the plot if she had not wanted to avoid shocking the public. Old Earnshaw sets off to Liverpool on foot because a letter has told him that his younger brother’s son, by a lady of mixed race in the Port of Liverpool, has been left destitute. He avoids scandal by not saying that this is his nephew, and leaves telling the secret until too late. This is all that is needed to explain the assumptions of the story.
William Empson (1966). Letter to Paunch. In Argufying: Essays on Literature and Culture, pp. 493–494.
But I think a better theory is that Heathcliff is Mr Earnshaw’s own mixed-race son. We can imagine that on previous trips to Liverpool he has maintained a mistress, but she has died leaving their son to his care. This would explain more convincingly why he was unwilling to tell the truth to his wife and family. It would also explain why Mr Earnshow “took to Heathcliff strangely, believing all he said […], and petting him up far above Cathy, who was too mischievous and wayward for a favourite” (IV), and why “they had christened him “Heathcliff”: it was the name of a son who died in childhood” (IV).
Earnshaw […] gives a vague and illogical report of finding the homeless and starving child in the Liverpool gutters. Earnshaw’s rationalization of the adoption seems weak […] Even in an eighteenth-century provincial slum, the waif must have had some protector. Mrs. Earnshaw considers her husband to be mad, and the narrator, tart Nelly Dean, expresses doubts through her manner of recounting the tale. […] The brief picture of Mrs. Earnshaw presented here would certainly supply an added motive for concealment of a child who could possibly be Earnshaw’s illegitimate offspring. She “was ready to fling it out of doors”; she grumbles and berates the exhausted traveler. How would such a woman have reacted to any honest admission of sinful adultery? Earnshaw could only bring a by-blow into the family by devious means, as long as his wife was still alive.
Eric Solomon (1959). ‘The Incest Theme in Wuthering Heights’. In Thomas A. Vogler ed. (1968). Twentieth Century Interpretations of Wuthering Heights, p. 111. New Jersey: Prentice-Hall.