Halfway through the first major UK retrospective of paintings by Tove Jansson, which opens this week at the Dulwich Picture Gallery, visitors will recognise some little blobby creatures in a glass case – the Moomins.

The stars of some of the most famous children’s books of the 20th century, they have become deeply familiar in their incarnations as fridge magnets, soft toys, on the tail fins of Finnish planes and in a newly opened museum in Finland. They have also appeared in cartoon strips and animations, with a new film coming at Christmas and a new animated series promised in 2019 featuring the likes of Kate Winslet, Rosamund Pike and Will Self.

The Moomins may not, however, have been how Jansson would have chosen her work to be defined. Their pottering around their flowery valley, and hibernating through the fierce Nordic winters until a messenger brings news of spring made her famous the world over, but they have completely overshadowed the reputation as a serious painter that she yearned for all her life, and which the Dulwich exhibition will try to rescue.

“The pictures are wonderful,” said the gallery’s director, Jennifer Scott. “I’ve surprised myself at how drawn I feel to them. She fits perfectly into one of the things we do best at Dulwich, which is to take a very unfamiliar name, or a name people think they know, and show a completely different aspect of their work.”

Despite the scores of paintings from private collections and Finland’s national gallery, the Ateneum in Helsinki, including a haunting last self-portrait painted years before Jansson’s death aged 87 in 2001, the Moomins have crept into half the exhibition space and taken over the final room.

The first Moomin book was published at the end of the second world war and was clearly in its shadow, a surprisingly dark fantasy of a world almost destroyed by catastrophic flood. Other books followed, but it was only when one was translated into English in 1951, and her creations became a cartoon strip for the London Evening News, that she became internationally famous.

Clare Simpson, the head of exhibitions at Dulwich, was helping Liisa Kantanen from the Ateneum set out the fragile models of the characters, beautifully made by Jansson’s life partner, the artist and craft worker Tuulikki Pietilä, and borrowed from a private collection. Directing the little figures to turn toward one another in conversation, she said: “I feel sorry for Tove really. The Moomins brought her fame and money, which bought her freedom, but they also cannibalised her time and creative energy and distracted her from what she considered her real work.”

The exhibition includes original artwork for the strip, believed long lost, which turned up in an uncatalogued envelope in the collection of the Cartoon Archive in Kent. After seven years writing and drawing the strip, Jansson was so drained by the work she handed it on to her brother, who kept it going until 1975.

Jansson was born into a family of hardworking artists in Helsinki in 1914 – her father was a sculptor, but most of the bills were paid by her mother’s illustration work – and earned money from magazine and book illustration from the age of 15.

The exhibition shows her covers for the satirical magazine Garm, including a wartime Christmas number of a dancing Hitler roaring for cake. Some include tiny hippo like figures, the first appearance in print of the Moomins, which she had been drawing since sketching them on the wall of a childhood holiday home.

The exhibition’s curator, Sointu Fritze, who is also chief curator at the Ateneum, said the Moomins had earned their place in the exhibition, even if they often made it hard for Jansson to be taken seriously as a painter at a time when hierarchies in art were still rigid.

“Although Tove Jansson was sometimes tired of the Moomins or frustrated to be known primarily as the ‘Moomin Mamma who can also paint’, she did take the work on Moomins as seriously, with a strong devotion, as her painting,” Fritze said.

“I think she was herself able to see her ouvre as a continuum and a whole, the sources of inspiration being very much the same for everything she did.”

• Tove Jansson 1914 - 2001, Dulwich Picture Gallery, 25 October 2017 - 28 January 2018