Since its creation in 1946 by British clergyman Wilbert Audry, Thomas the Tank Engine has charmed generations of children, imparting gentle wisdom while keeping alive the romantic nostalgia of British railways.
But even the Island of Sodor cannot remain in aspic forever, and owners Mattel have announced that the sleepy setting is to be shaken up by an influx of foreign characters.
In a nod to cultural diversity in modern life, Thomas is to make 14 new friends from countries such as India, Brazil, China and Mexico.
It is the latest effort by Mattel to expand the reach of the franchise which already brings in more than pounds 500 million in annual retail sales, one of the largest of any toy range in the world.
However the announcement of the new cast has led to fears that the ambience of the programme could be lost. There are also worries about cultural stereotyping.
Raul of Brazil is described as "feisty", "strong" and "agile" while Yong Bao of China is "driven to achieve" and "make progress". Ashima of India is "happy to help out" while Carlos of Mexico is "proud" and "always wearing a smile" as well as having the type of eyebrows last seen on Frida Khalo.
Tracey Van Slyke, a researcher in social justice and pop culture, has previously accused the programme of sending out "pretty twisted, anachronistic messages" because the engines are forced to perform tasks "dictated by their imperious, little white boss".
She said of the new characters: "I applaud the idea, but am concerned about execution. There is a danger in reducing very complex countries and peoples to singular characteristics. If the trains are only defined by cultural stereotypes, the result will be a calculated, and destructive, nod to diversity and inclusivity".
There are also fears that the traditional feel of the programme could be lost. Psychologist Dr Aric Signman said one of the attractions of the show was its slow-pace and small cast.
"Children do not benefit from a lot of variety," he said. "If there are going to be a lot of new characters then it will be more difficult for children to invest in the narrative and to feel connected."
Rev W Awdry, a vicar in the parish of St Nicholas, in Kings Norton, Birmingham, wrote his first story about an anthropomorphised train in 1942 for his son Christopher who was ill with measles.
The following year, having written two further stories, he was encouraged by his wife, Margaret, to send them to publishers. The resulting book, The Three Railway Engines, was published on May 12 1945 and was an instant success. The Rev W Awdry, who died in 1997, wrote 26 Railway books and saw his creation become one of the world's most successful children's brands.
Veronica Chambers, his daughter, said: "I think [Mattel] have tried to expand Thomas cultural outlook."
Asked if her father would have approved, she added: "What he would have been pleased about was to think that Thomas is still bringing such joy and pleasure to grown-ups all over the world. And in everything Mattel have done they have strictly adhered to the right railway practice. All the new characters, introduced are based as far as possible on actual locomotives."