Bert, William and Tom are minor antagonists in the 1937 novel, The Hobbit and it's various adaptations and minor characters in The Lord of the Rings, making a cameo appearance as statues in The Fellowship of the Ring. In the novel, they capture Thorin and his company (except for Bilbo in the book). They are Stone-trolls who try to cook the Dwarves; however, Gandalf imitates each of them, causing them to fight. They bicker the rest of the night and are exposed to sunlight, and immediately transform back into the rocks of the mountain they were once forged from, forever remaining statues.
Nearly seventy years later (sixty in the film), Aragorn sets up camp near the trolls when he and his companions, Frodo Baggins, Samwise Gamgee, Meriadoc Brandybuck and Peregrin Took
are on theit way to Rivendell to seek Elrond to heal Frodo, who had been injured by the Witchking of Angmar, having been stabbed by a Morgul blade