What is the name of the first Harry Potter book’s main villain, created by J.K. Rowling?

The main villain of the first Harry Potter book created by J.K. Rowling is Lord Voldemort.

Voldemort is the feared name used by Tom Riddle, a former Hogwarts student who seeks magical power and immortality. In Harry Potter and the Philosopher’s Stone, he has not fully regained his body and is working through Professor Quirinus Quirrell. The first book gradually reveals that Voldemort is connected to Harry’s lightning-shaped scar and the attack that killed Harry’s parents.

Across the series, Voldemort becomes the central antagonist. His attempts to avoid death lead to the creation of Horcruxes, objects containing fragments of his soul. This makes the later conflict more complicated than a simple duel between two wizards.

Gellert Grindelwald is another dark wizard in Rowling’s wider Wizarding World, but he belongs mainly to an earlier generation. Lucius Malfoy is a Death Eater and Voldemort’s follower, not the series’ principal villain.