Petunia (Evans) Dursley
I was the only one who saw her for what she was -- a freak! But for my mother and father, oh no, it was Lily this and Lily that, they were proud of having a witch in the family!"
-- Petunia to Harry (PS4)
Aunt Petunia is Lily (Evans) Potter’s older sister, and the wife of Vernon Dursley. The Dursleys live at number four Privet Drive, Little Whinging, Surrey. She is a tall, very thin blond with a long neck and an angular face.
Estrangement and bitterness
When they were younger, Petunia and Lily were very close, so when Lily began to show signs that she was a witch, Petunia was frightened; when Lily got the invitation to Hogwarts, Petunia was so unhappy about being separated from her sister that she wrote a letter to Dumbledore and asked if she could attend (of course, she couldn't). By the time Lily and James were killed, Petunia's loneliness and disappointment had hardened into jealousy and an utter revulsion of magic. It didn’t help that both Lily and Petunia learned first about magic from an odd, intense neighborhood boy named Severus Snape; wizardry will always be “freakish” to Petunia (PS4). Any mention of her sister upset her.
and Dumbledore's protection chrm
As an adult, Petunia is a nosey gossip who dotes on her son Dudley, keeps an obsessively immaculate house, and defers to her smug, blustering husband. Uncharacteristically, she also agreed to Dumbledore’s written request to take Harry in when he was orphaned (PS1).
We don't know exactly what Dumbledore wrote, but according to him, it informed Petunia that by taking Harry in she was providing him with powerful magical protection. Dumbledore told Harry: "You need return there only once a year, but as long as you can still call it home, whilst you are there he cannot hurt you. Your aunt knows this. I explained what I had done in the letter I left, with you, on her doorstep. She knows that allowing you houseroom may well have kept you alive for the past fifteen years." (OP37).
But she didn't promise to love him; from the beginning, Petunia's treatment of Harry is cruel and reprehensible (allowing Harry's older cousin to pinch and prod him). In stark contrast to her overindulgence of her own child, Harry is treated like an unwanted servant (CS2).
If Petunia's feelings for Harry ever softened, she never showed it. When Harry reached his majority and they parted for (perhaps) the last time, Petunia said good-bye and could not bring herself to say more (DH3).
Petunia in the Movies
The role of Petunia Dursley is played by Fiona Shaw (IMDb).