As the tweet from McSweeney's said, "We'll be roaring our terrible roars today."
The popular children's book author wrote "Where The Wild Things Are" in 1963. He won a Caldecott Medal for the book in 1964, and was adapted into a movie in 2009.
According to The New York Times, a posthumous picture book, "My Brother's Book," is scheduled to be published in February 2013.
Sendak also created costumes for ballets and staged operas, including the Czech opera "Brundibar," which he also put on paper with collaborator Pulitzer-winning playwright Tony Kushner in 2003.
He designed the Pacific Northwest Ballet's "Nutcracker" production that later became a movie shown on television, and he served as producer of various animated TV series based on his illustrations, including "Seven Little Monsters," "George and Martha" and "Little Bear."
"I write books as an old man, but in this country you have to be categorized, and I guess a little boy swimming in the nude in a bowl of milk (as in `In the Night Kitchen') can't be called an adult book," he told The Associated Press in 2003.
"So I write books that seem more suitable for children, and that's OK with me. They are a better audience and tougher critics. Kids tell you what they think, not what they think they should think."
During that 2003 interview, Sendak also said he felt as if he were part of a dying breed of illustrators who approached their work as craftsmen. "I feel like a dinosaur. There are a few of us left. (We) worked so hard in the `50s and `60s but some have died and computers pushed others out."
"Kids don't know about best sellers," he said. "They go for what they enjoy. They aren't star chasers and they don't suck up. It's why I like them."
I've read a zillion of your books, Maurice, and used to eagerly anticipate each new Little Bear volume as it came out, while eating my Chicken Soup with Rice. Thanks for making all our childhoods -- and adulthoods -- all that much more imaginative and grand, and please R.I.P.