Who are the trolls under the bridge?

The trolls under the bridge are characters from the classic fairy tale "The Three Billy Goats Gruff." In the story, they are depicted as large, menacing creatures who guard a bridge and threaten to eat anyone who tries to cross it. The three billy goats ultimately outsmart the trolls, allowing them to pass safely and reach the lush grazing land on the other side. The tale serves as a metaphor for overcoming obstacles and using cleverness to defeat challenges.