The look of the trolls in the film is influenced by painters like Theodor Kittelsen (Forest Troll; Christian Troll; Troll at the Karl Johan Street) and John Bauer (Root Trolls; Look at them, mother Troll said....).
The film contains several references to old Scandinavian folklore. For example, the goats on a bridge and a troll under it are a reference to the "Three Billy Goats Gruff". At one point Kalle mentions an eating competition, a reference to the story "Askeladden".
The movie contains several characters played by Norwegian comedians: Otto Jespersen (the troll hunter), Knut Nærum (the power plant supervisor), Robert Stoltenberg (the Polish bear supplier), and Hans Morten Hansen (Finn, the troll hunter's boss) are all high profile comedians.
Trollhunter contains many references to Norwegian culture and Norwegian folktales e.g. the belief that there are different species of trolls, trolls having a tail, multiple heads, the ability to smell a Christian's blood, trolls eating rocks, but loving meat and sometimes being man-eaters. The trolls are also described as big, old, strong, but slow and dim-witted, turning to stone when exposed to sunlight.
The film also has several specific references to some traditional fairy tales e.g. Boots Who Ate a Match With the Troll, Three Billy Goats Gruff, Soria Moria Castle.
A painting by Theodor Kittelsen based on the Soria Moria Castle fairy story is used as a backdrop on one of the trips they do in the film (Thomas stands in the same pose and asks his friends "Do I look like that famous painting?").