The moon-faced creation, who has spawned a multi-billion dollar industry, began her birthday by trying her hand as manager of the Mitsukoshi department store in Tokyo’s glitzy Ginza district.
Clad in pink from head to toe with a customary bow on her head, a human-size Kitty showed up at an in-house meeting at the store, drawing cheers and applause from hordes of employees.
She bowed to the staff, who bowed back.
The mouthless character did not speak but waved and struck poses, sending many on the floor blurting out “kawaii!”, the Japanese word for “cute”.
As the store opened, she greeted the first wave of customers, many of whom hugged the character and posed for pictures.
Kitty, who adorns everything from pencil cases to pyjamas the world over, also celebrated her birthday with fans at her creators’ theme park Sanrio Puroland in western Tokyo.
Surrounded by hundreds of admirers, she performed dances with other characters including her twin sister Mimmy.
The Keio Plaza Hotel chain, meanwhile, opened Hello Kitty hotel rooms in Tokyo on Saturday, decorated floor to ceiling with pictures of the cuddly character.
On the other side of the Pacific, a Hello Kitty Convention in the Little Tokyo district near downtown Los Angeles has opened for a four-day run through the weekend, expecting to draw some 25,000 fans.
First released in 1974 and appearing on a coin purse the following year, Hello Kitty now features on more than 50,000 products in 130 countries and territories.
Creator Sanrio says cute-loving adults are the main customers driving business.
Despite her years, the timeless character, who insists “you can never have too many friends”, is still exploring new frontiers.
Kitty went on a space mission this year aboard a satellite and Sanrio is launching a line of Kitty products for men next year, possibly before Valentine’s Day.
She has also appeared on a dress made for eccentric US pop diva Lady Gaga, while Taiwanese airline EVA Air marked the 40th anniversary by launching a Hello Kitty plane, complete with Kitty-themed airline food and stewardess uniforms.
Fans were stunned in August when it emerged that Kitty is in fact not a cat, but a girl.
Sanrio says it has been saying all along that she is a “happy little girl with a heart of gold” — despite her whiskers and pointy ears.
“Kitty was making telephone calls and had a goldfish friend from the very beginning,” a Sanrio spokesman has said.
“It is a 100-percent personified character… Barring her cat face, she does exactly what humans do.”
According to her official biography, Kitty was born in a London suburb on November 1, 1974 to parents George and Mary. She has a cat named Charmmy Kitty. (AFP)