George and Martha by James Marshall. George and Martha are best friends, and James Marshall’s storybooks show us what that means. They tell the truth to each other, even if it hurts; they respect each other’s privacy; they learn what it means to be friends. They are also hippos, and that makes the illustrations to these stories lots of fun. James Marshall wrote the first book (George and Martha) in 1972.
Five sequels followed in the next 15 years. I loved the first one: the clever illustrations were imperative to the humor and plot of the five very short stories. The subsequent books, while equally ridiculous (i.e., humorous), didn’t charm me as much. You can also buy a book with all six collections of George and Martha stories.