It was 35 years ago that Mr Tickle first made an appearance, kicking off generation after generation's love for the Mr Men and the Little Miss books.
By Keily Oakes
BBC News entertainment reporter
The Mr Men were the creation of Roger Hargreaves who came up with the Mr Tickle character when his young son Adam asked what a tickle looked like.
Now decades later there are more than 40 Mr Men characters and 30 Little Misses.
Mr Tickle started the whole Mr Men phenomenon
An exhibition to mark the anniversary has opened at the Animation Art Gallery in London.
Adam took over the Mr Men empire in 1988 when his father died suddenly at the age of 53.
He had never attempted to draw any of the Mr Men before he was plunged into the world of children's fiction.
"My mum says I have drawn from as soon as I could hold a pencil. I did a year at art college but really it was just a hobby until I got involved with the Mr Men," said Adam.
"I had never drawn the Mr Men before he died. It took a long time to learn to draw them, my dad drew in a different style to me. I think it took about three years to learn to draw them."
The Mr Men and Little Miss book titles were sold to entertainment group Chorion in 2004 in a £28m deal. Adam joined the company as a part-time creative consultant, which is the part of process he enjoys.
"I have been working on the Mr Men books for about 16 years, nearly as long as my dad, which is a strange thought as I never considered working on them.
"I only found out I was going to take over after my dad died, but there was a company to run and I was at a bit of a crossroads in terms of career.
"I now don't work on Mr Men every day, so I'm able to pursue my other ambition which is oil painting, mainly landscapes."
The newer books are still published with the name Roger Hargreaves on the front of the book.
"It doesn't actually say 'by Roger Hargreaves' but it has his name on the front of the new books because I feel his name is what Mr Men are synonymous with, it's part of the brand in a way," said Adam.
"On the inside it says 'written and illustrated by Adam Hargreaves'. It's not trying to be misleading, it's really just part of the brand."
Little Miss Naughty is Adam Hargreaves favourite Little Miss character
The original books written from 1971 are the ones that continue to be published to this day.
They have never been re-illustrated, except for one page of Mr Silly which was redrawn while Roger was still alive, because the character was smoking a cigar, which was considered too un-PC for young children.
Adam Hargreaves said: "I don't think they have dated at all.
"They are possibly not as contemporary as the new ones because there are technological differences out there that have changed the way the world looks, so they get incorporated in the new books, like mobile phones.
"The characters themselves have not dated because they don't sit in a particular time frame."
Adam would like to see the Mr Men franchise continue for another 35 years, breaking into new countries, particularly in the US where they have had a degree of success in the past but have not been heavily promoted.
"I think there are elements of the Mr Men that are quintessentially English in the stories but the characters are international because the human emotions, characteristics are there in every culture in every language - funny, happy, naughty, is something that is very easily translated."
Mr Birthday, who likes parties, was created to mark the 35th anniversary of the Mr Men
For the latest books, Mr Birthday and Little Miss Birthday, Adam returned to the first books written by his father for inspiration.
"I tend to go back to the original stories just to get a feel of the stories and the way he wrote. There's a degree of formula to the Mr Men so I always like to remind myself of them.
Adam has two children, aged 12 and 18, and admits it was only his youngest Jacob who really enjoyed the Mr Men.
"Both are arty so there's every chance they could take over from me. Hopefully that's a long way off."
The Mr Men and Little Miss exhibition is running at the Animation Art Gallery in London.