All the Whos down in Whoville enjoy celebrating Christmas with much happiness and joy, except for the cynical and misanthropic Grinch (Jim Carrey), who hatefully despises Christmas and the Whos with great wrath and occasionally pulls dangerous and harmful practical jokes on them. As a result, no one likes or cares for him. Meanwhile, six-year-old Cindy Lou (Taylor Momsen) believes everyone is missing the point about Christmas by being more concerned about the gifts and festivities. Cindy Lou eventually learns that the Grinch is real and becomes interested in his history; she asks everyone what they know about him, and soon discovers that he has a tragic past.
The Grinch actually arrived in Whoville by mistake when he was a baby, and was adopted by two elderly sisters. Although he showed some sadistic tendencies as a child, he was rather timid and not the cruel, selfish person he would become; he was ridiculed by his classmates (particularly by Augustus May Who, the current Mayor of Whoville) because of his appearance, with the exception of Martha May Whovier, who was courted by both the Grinch and May Who. One Christmas season, he made a gift for Martha, but attempted to shave his face, cutting himself and when the school saw his face covered with shaving tape the next morning, they laughed at him. He lost his temper, went on a rampage and ran away to live on Mt. Crumpit.