What is the name of the potion that allows the drinker to turn into someone else?

The potion that allows the drinker to turn into someone else is Polyjuice Potion. It temporarily transforms the drinker into the physical form of another person, making it one of the most strategically important—and dangerous—potions in the Harry Potter series.

The potion requires difficult preparation and ingredients, including lacewing flies, leeches, powdered bicorn horn, knotgrass, fluxweed, and a piece of the person being imitated. That final ingredient determines whose appearance the drinker takes. In Harry Potter and the Chamber of Secrets, Harry, Ron, and Hermione use it to impersonate Slytherin students while investigating the Chamber of Secrets.

Polyjuice Potion changes appearance but does not transfer the target's memories, personality, or magical abilities. Hermione's accidental transformation into a cat-like hybrid happens because she mistakenly adds cat hair. The potion is easily confused with Felix Felicis, which brings luck, Amortentia, a powerful attraction potion, and Veritaserum, which compels truth-telling.