He cast a spell on the world — and left readers wanting more.

Monday marks the 20th anniversary of when "Harry Potter and the Philosopher's Stone," the first in J.K. Rowling's fantasy book series, was published in the United Kingdom in 1997. The books since then have come wildly popular.

A blockbuster series of movie adaptations made stars out of actors Daniel Radcliffe, Rupert Grint, and Emma Watson, who starred as Harry and his friends Ron Weasley and Hermione Granger, respectively.

Here's the reaction on social media to this pop culture milestone: