Petunia Dursley is Harry's maternal aunt, Lily Potter's older sister, Vernon's wife, Dudley's mother and Marge's sister-in-law. She is described as a bony woman with a "rather horsey" face and a very long neck, and spends most of her time spying on her neighbours. Her eyes are large and pale, quite unlike Lily's. Her whole family is made up of Muggles, except for Lily, a Muggle-born witch. According to Petunia, her parents were proud of having a witch in the family, but Petunia saw her sister as a freak. In fact, she was envious and resentful of Lily's magical abilities and went so far as to write to Dumbledore, pleading to be allowed to enter Hogwarts. Dumbledore gently denied her enrollment. Afterwards, Petunia grew bitter towards the school and, by extension, towards the wizarding world in general. She had no contact with Lily after her marriage to James Potter and the birth of her nephew, Harry, though she did send the family a "horrible vase" that baby Harry broke while riding on a toy broom. The gift echoes Harry's Dursley-sent Christmas presents, which are never pretty or welcome.
Petuunia has more knowledge of the wizarding world than she is initially willing to admit. After the Dementors attack Harry and Dudley, Petunia states that she knows Dementors guard the wizard prison, Azkaban. When Harry and the rest of her family look at her strangley, she explains that she heard "that awful boy" telling Lily about them years ago. Harry assumes that the "awful boy" was his father, James, but in Harry Potter and the Deathly Hallows, he learns via flashback memories that it was actually Severus Snape, who knew both Lily and Petunia when they were children. On one occasion, Petunia, but mostly her husband almost send Harry of their house, but she receives a Howler from Albus Dumbledore and decides not to send the boy away due the agreement she had made with Dumbledore.
Before the Dursleys leave Privet Drive to go into hiding, Petunia almost wishes Harry good luck, suggesting that she does feel a tiny sense of familial attachment to her nephew; however her self-imposed dislike of magic prevents her from doing so, and she leaves without a word. In the film version of Harry Potter and the Deathly Hallows - Part 1, she leaves Harry without showing any sentiment; however, in a deleted scene on the Blu-ray/DVD release, Petunia shows acknowledgment of the wizarding world, and ultimately deep sadness and remorse for the loss of her younger sister Lily.
Actress Fiona Shaw portrays adult Petunia in the films, with Ariella Paradise playing her as a child.