Who else commits acts of revenge in Wuthering Heights other than Heathcliff and for what purpose?
I would want to argue that Catherine (the elder, as opposed to her daughter) likewise engages in acts of petty and vindictive revenge when she doesn't get her own way. The best example of this comes after Heathcliff and Linton fight over her, and she believes that nobody cares about her because of the way that Linton only spends time in his library, so she determines to starve herself to death to make both her husband and Heathcliff sorry for their actions. There is something childish about this, but the way that Catherine proceeds and succeeds with her plan shows that this is a highly self-absorbed act of revenge. Note what she says to Nelly about her determination to make her husband and Heathcliff suffer:
"Nelly, if it be not too late, as soon as I learn how he feels, I'll choose between these two: eitehr to starve at once--that would be no punishment unless he had a heart--or to recover, and leave the country."
She then goes on to say just a couple of paragraphs later, that "If I were only sure it would kill him... I'd kill myself directly!" Her actions in starving herself are carried out in terms of achieving revenge for the lack of care and love she feels slighted by. Heathcliff is definitely not the only character who embarks on courses of revenge.