The Mr Men are celebrating their 40th birthday today.
The colourful characters have been delighting children since Mr Tickle first appeared on bookshelves in 1971.
Since then, he has been joined by Mr Bump, Little Miss Sunshine, Mr Messy and other characters in one of the most recognisable series in the world.
Author Roger Hargreaves originally created Mr Tickle after his six year-old son, Adam, asked him: "Daddy, what does a tickle look like?"
The resulting illustration launched the popular books, which have since been translated into 15 different languages globally.
Adam Hargreaves, now 47, said: "It is truly incredible that something so personal to my father went on to become such a global phenomenon.
"If he were alive today, I think he would be ecstatic to see how popular his creations have become.
"My dad managed to capture basic human characteristics that can be recognised as part of each and every one of us.
"We've all been a Mr Happy, Mr Funny and even a Little Miss Naughty at times."
An astonishing 120 million Mr Men and Little Miss books have been sold worldwide - an average of one every 2.5 seconds.
In the last decade Roger Hargreaves became the third best- selling British author, topped only by Harry Potter author JK Rowling and Dan Brown, who penned the Da Vinci Code.
The average household in the UK owns more than one Mr Men or Little Miss book, with total sales in the UK alone now at more than 75 million.