Tove Jansson (1914-2001) is a Swedish-speaking Finnish author, most notably known for her Moomin character books, which she published starting in 1945. Though she is often remembered as a children literature author, she has published extensively also for adult audiences.
The popularity of the hippopotamus-resembling Moomin characters was undoubtedly due to the storyline, which was doubled by Tove Jansson‘s own illustrations. Since 1992, they have become a constant presence on stamps, from their native Finland and off to the world.
Åland Islands
Åland Isl. issued this stamp featuring the art of Tove Jansson in the year 2007.
Japan
I would be totally unaware of the popularity of the Moomin characters in Japan if it were not for their already two-time stamp issue representing the characters.