J.K. Rowling at the Southbank Centre in London in 2012.
Lefteris Pitarakis—AP
October 31, 2014 7:28 AM EDT

Just in time for Halloween, Harry Potter creator J.K. Rowling published a new essay Friday about one of her greatest villains: the Hogwarts professor and witch, Dolores Umbridge.

The nasty Umbridge is one of the characters for whom Rowling “feel[s] the purest dislike,” according to the 1,700-word essay, posted to her website Pottermore (account required). “Her desire to control, to punish, and to inflict pain, all in the name of law and order, are, I think, every bit as reprehensible as Lord Voldemort’s unvarnished espousal of evil.”

Rowling also reveals that Umbridge is actually based on a real-life person, though the author is careful not to reveal her identity. She does reveal that “[t]he woman in question returned my antipathy with interest. Why we took against each other so instantly, heartily and (on my side, at least) irrationally, I honestly cannot say.”

Harry Potter fans have long been familiar with Umbridge and her cruel ways, as the character was first introduced in the 2003 novel Harry Potter and the Order of the Phoenix. At the time, Umbridge was the Senior Undersecretary to the Minister for Magic.

But Rowling also reveals new details about Umbridge in her Pottermore essay, including the fact that Umbridge is a “half-blood”—the daughter of a wizard and a Muggle (a regular person). The author also writes that when Umbridge forced Harry, who was in detention at the time, to cut the words “I must not tell lies” onto the back of his hand, she became the only person other than Lord Voldemort to leave a permanent physical scar on the boy wizard.

In addition to the new essay about Umbridge, Rowling has also published more brand new writing to Pottermore for Halloween and to celebrate the launch of The Order of the Phoenix onto the website. The new entries include details about the creatures Thestrals, the history of the wizarding prison Azkaban, Rowling’s thoughts on professor Sybil Trelawney and an introduction to the wizarding practice of Naming Seers.

Read next: Harry Potter Site Teases New J.K. Rowling Story

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