The world of author and illustrator Dr Seuss is one in which nothing and everything makes sense. It's a place of strange cats invading homes and causing havoc, of authoritarian turtle kings, of tales told in a rhythm that trips irresistibly off the tongue. Most importantly - and surely the reason his books have sold over 600 million copies - it's extremely funny.
Born in Massachusetts in 1904, Theodor Seuss Geisel adopted his pen name while at university, in a nod to his father's thwarted desire for him to practise medicine. He studied literature at Dartmouth College and Oxford University before beginning his career in 1927 as an illustrator and political cartoonist.
After World War II his focus shifted to children's books: he would go on to write 44 books for young readers, from The Cat in the Hat and How the Grinch Stole Christmas! to Oh, the Places You'll Go!.
Following an architectural revamp, the Discover Children's Story Centre in London is re-opening this month with an exhibition celebrating Dr Seuss' work and showing some of his original sketches.
Boundless ideas and energy jump around the pages of his sketchbooks. You can see the text and image coming into being together: typewritten drafts of the story are pasted on to the same pages as drawings, with developing notes and edits for both.
Geisel's effervescent visual style is just as distinctive as his writing, and it's thrilling to watch both of them emerge as equally important ingredients in his work.
Although they have delighted generations of children, the books' appeal lasts long into adulthood. Barack Obama is a fan: "Pretty much all the stuff you need to know is in Dr Seuss," he said this year when launching a national reading initiative, praising the "homespun, basic virtues" behind the wild imagination of Geisel's writing.
David Cameron has named The Lorax, an environmental parable, as his favourite children's book.
Geisel, who died in 1991, used to tell people that he never started writing with a moral in mind, because "kids can see a moral coming a mile off". But though outwardly anarchic, his stories contain no shortage of life lessons. Green Eggs and Ham is about how you shouldn't knock something until you've tried it, while The Sneetches makes a stand against racial discrimination. Oh, the Places You'll Go!, the last book written before Geisel's death, is a glorious pep talk for attacking life as one big adventure, while being ready for the struggle of its darker moments: "You will come to a place where the streets are not marked/ Some windows are lighted/ But mostly they're darked". It's moving, uplifting, and treats young readers with respect.
In teaching millions the joy of literature, Geisel also opened up a wonderfully unique perspective on the world, where life is funny and beautiful, and where topsy-turviness shows us how things should be.
As the author himself once said: "If you can see things out of whack, then you can see how things can be in whack."
The Fantastic World of Dr Seuss is at Discover Children's Story Centre, London, from today.