The story
Named after the main character in a children's book by Dr. Seuss, How the Grinch Stole Christmas! (1957). Coined as early as 1953, the term was initially used for a fictitious bird named the "Beagle-Beaked-Bald-Headed Grinch" in Scrambled Eggs Super!; it became associated with the character in a poem published in the May 1955 issue of Redbook, "The Hoobub and the Grinch". Likely a corruption of grouch.
Etymology from Wiktionary, CC BY-SA 4.0.