Wuthering Heights is a variation on the Rags to Riches plotline. Heathcliff is (supposedly) an orphan who is brought into the home where he experiences abuse and neglect. Though Mr. Earnshaw loves him (too much, it seems), his new brother Hindley is deeply envious and sets out to make Heathcliff miserable. Rather than running away and losing the one home he has, Heathcliff bonds with Catherine, and together they find comfort and respite in the moors.
When Heathcliff loses Catherine to Edgar, he leaves Yorkshire. He possibly goes into the army or travels to America – no one knows for sure. What's important is that he returns with money, and this initial financial gain sets him up to accumulate more.
All the money in the world can't win Catherine – or keep her alive. So when he loses the one person he loves (and who loves him), Heathcliff can only think about punishing Hindley and Edgar Linton and taking possession of the two houses.
We finally see the depths of Heathcliff's cruelty as he sacrifices his own son's health and happiness in the service of his revenge. Then suddenly, he loses interest in sadism and begins to show some vulnerability and decency.
In death, Heathcliff finally gets what he wants – a reunion with his beloved Catherine. Brontë suggests that they will haunt the moors together, enjoying the countryside that provided such a source of tranquility and strength for them as children.