The story
From the donkey in A.A. Milne's books Winnie-the-Pooh and The House at Pooh Corner, whose name is onomatopoeic from a donkey's bray (compare hee-haw).
Etymology from Wiktionary, CC BY-SA 4.0.
Eeyore
Today it means: An excessively negative or pessimistic person. Full definition →