Who created them, and when
The Moomins were created by Tove Jansson, a Finnish author and illustrator from a Swedish-speaking Finnish family, who first introduced the characters in her 1945 novel The Moomins and the Great Flood. Jansson began developing the Moomin world during the Second World War, using it partly as an escape from the anxiety of the period — a detail that shows up later in some of the more melancholic, disaster-tinged themes running through the later books.
Not hippos
Despite the resemblance, Moomintrolls are not hippos. Jansson invented them as their own fictional species, loosely descended from Scandinavian troll folklore rather than any real animal. The core cast built out around Moomintroll includes Moominmamma and Moominpappa, his easygoing parents; Snufkin, a wandering, guitar-playing free spirit; Little My, a small and famously blunt troublemaker; and Snorkmaiden, Moomintroll's on-and-off love interest. Across nine books, a picture book and a long-running comic strip, Jansson built out a full valley of recurring characters, each with a distinct, well-defined personality.
From books to a global cartoon
The Moomins reached a much bigger international audience through animation, especially a 1990 Japanese-Finnish co-produced anime series that became hugely popular across Japan and much of Europe. That adaptation is a large part of why Moomin merchandise, cafes and pop-up stores are now just as visible in Tokyo as they are in Helsinki, and why the franchise has a genuinely global fanbase well beyond Finland's own population.
Where to see them in Finland
Naantali, a small town on Finland's southwest coast, is home to Moominworld, a theme park built directly around the books, where costumed actors play Moomintroll, Snorkmaiden and the rest of the cast. Tampere, further inland, houses the Moomin Museum, focused on Tove Jansson's original artwork and manuscripts rather than the theme-park experience. Between the two, Finland has effectively built a small tourism industry around one author's wartime creation — a fairly unusual example of a children's book series becoming genuine national cultural infrastructure.