“These ancient creatures might be found in the Valley of the Living Rock, but only if they want to be found. Trolls are masters of minerals and yielders of the night sky. They are also overbearing, loud, meddlesome, inappropriate, and heavy―really heavy. But they mean well and love well.”
Most of the trolls appear to be loving and family-oriented, such as when Bulda adopts Kristoff and Sven, and when she and the other trolls try to convince Anna to marry him. Sometimes, they seem crude and a bit intrusive, but their affectionate teasing only endears them to Anna. They consider Kristoff and Sven to be part of their family, and they treat them as such.
Once Upon a Time
In Once Upon a Time, the Trolls are seen with Pabbie, only in bowl form, in a flashback when Elsa and Anna visit them for to obtain information on the death of their parents and when Anna and Belle visit Pabbie to get answers to their mothers. A statue of a troll is also seen in the present day, when Emma and Hook purchases Elsa.
It should be noted that the crystal necklaces each troll wears represent a gender or position in their culture:
Male trolls wear blue and green crystals.
Female trolls wear pink and red crystals and also wear flowers in their hair.
Pabbie, Bulda's father and Kristoff's adoptive maternal grandfather, is the only troll to wear yellow crystals, possibly signifying his role as the leader.
When they speak, their crystal necklaces light up, as seen in "Fixer Upper".
The troll children show Kristoff what they have achieved. One grows a mushroom on its back and another has earned a fire crystal.
According to the book The Art of Frozen, the trolls' magical crystals channel the aurora borealis.
Contrary to the portrayal of trolls in many Scandinavian cultures, that being they are big, cruel, stupid and rarely helpful, these trolls in Frozen are small, kind, wise, and very helpful to those who need it.
It is possible that these trolls are based off the robbers that appear in the original tale of The Snow Queen. In the original story, these robbers capture Gerda (Anna), who becomes the new playmate of the youngest robber, the Robber Girl (whom Kristoff is based off of), who later releases her after hearing Gerda describe her mission to rescue Kai from the Snow Queen (both of which Elsa appears to be based on). Unlike the dangerous robbers in the original story, the trolls here are helpful and mean the protagonists no harm.