Physically, Eeyore is described as an "old grey donkey." In Ernest H. Shepard's illustrations, he appears to be about chin-high to Pooh and about hip-high to Christopher Robin. He has a long, detachable tail with a pink bow on the end, of which he is very fond, but that he is also prone to losing (Owl once mistakes it for a bell-pull). Christopher Robin is able to reattach the tail with a drawing pin.
His name is an onomatopoeic representation of the braying sound made by a normal donkey, usually represented as "hee haw" in American English: the spelling with an "r" is explained by the fact that Milne and most of his intended audience spoke a non-rhotic variety of English in which the "r" in "Eeyore" is not pronounced as /r/.
Eeyore is apparently able to write, or at least recognize letters such as the letter A that he teaches to Piglet in the fifth chapter of The House at Pooh Corner. He spells his own name "eoR" when signing the "rissolution" that the animals give to Christopher Robin as a farewell present in the final chapter of The House at Pooh Corner. Eeyore also wrote the awkwardly-rhymed poem called "POEM", which appeared on the "rissolution", making him the only character in the Winnie-the-Pooh books other than Pooh himself who attempts to write poetry. Eeyore is also surprisingly good at the game Poohsticks, winning more times than anyone else when it is played in the sixth chapter of The House at Pooh Corner.
Eeyore lives in the southeast corner of the Hundred Acre Wood, in an area labeled "Eeyore's Gloomy Place: Rather Boggy and Sad" on the map in the book. He has a stick house therein, which collapses rather regularly, called The House at Pooh Corner. Pooh and Piglet built it for him after accidentally mistaking the original house that Eeyore built for a pile of sticks.
He has a poor opinion of most of the other animals in the Forest, describing them as having "No brain at all, some of them", "only grey fluff that's blown into their heads by mistake" (from chapter 1 of The House at Pooh Corner).
Eeyore's favorite food is thistles. On Eeyore's birthday, he is given an empty honey jar from Pooh; a popped green balloon from Piglet, and a note from Owl.
Eeyore also appears in the Winnie-the-Pooh cartoons popularized by The Walt Disney Company.
He was ridden by Rabbit in his search for train "borrowers" in The Tigger Without A Name and The Pooh With A Name. Nearly all of Eeyore's houses in the cartoons have been bounced down. Eeyore is not good at rebuilding the houses; woozles bounce on them. Yet he soldiers on and rebuilds them time after time. Despite his depressive nature, Eeyore is capable of great compassion, which is shown when he grows a plant that Rabbit, a master gardener, was unable to grow, just by showing the plant a little love.
Eeyore has also been featured in a number of movies: Piglet's Big Movie, The Tigger Movie and Pooh's Heffalump Movie. He appears at the Walt Disney Parks and Resorts for meet and greets. His catchphrases are "Thanks for noticin' me" and "Ohhh-kayyy".