Tom, Bert, and William

"What are yer?"

- William the troll, in The Hobbit: Roast Mutton

"Bilbo Baggins, a bur—a hobbit."

- Bilbo, Ibid.

"A burrahobbit? What's a burrahobbit got to do with my pocket, anyways?"

- William, Ibid.

Tom, Bert, and William ("Bill") Huggins were three Trolls that Bilbo Baggins encountered in the Trollshaws, in Eriador, while with Thorin and Company on their quest to regain the Lonely Mountain (Erebor). Like most of their kind outside of Mordor, they were vagabonds who robbed, stole, and killed for what they needed or wanted. Their age is unknown. They were destroyed by sunlight which turned them to stone with the aid of Gandalf's magic.

In The Hobbit
When Bilbo tried to pick William's pocket to test his skill as a burglar, William's purse squealed, alerting him. The trio of Trolls captured Bilbo who, almost revealing himself as a burglar, identified himself as a "burglar-Hobbit", which they mistook for a "Burglar-hobbit". Eventually all of the dwarves in Thorin's company came looking for Bilbo, and were waylaid by the trolls and put into sacks. The trolls then discussed ways to kill and eat the dwarves, until Gandalf came and mimicked the Trolls' voices, starting a fight amongst them. He kept them arguing about how to cook the dwarves until dawn came, and the Sun turned them into stone before they could get to cover. Afterward, Thorin and Company found and explored Tom, Bert, and William's cave.

There is some confusion as to what breed of Troll they were, some saying Stone Trolls—this confusion being easily illustrated by the fact that several different pages of this wiki detailing breeds of Troll list these three as members of that particular breed.

In The Lord of the Rings
"There stood the trolls: three large trolls. One was stooping, and the other two stood staring at him. Strider walked forward unconcernedly. ‛Get up, old stone!’ he said, and broke his stick upon the stooping troll. Nothing happened."

- Strider, Lord of the Rings

"Well! We are forgetting our family history! These must be the very three that were caught by Gandalf, quarrelling over the right way to cook thirteen dwarves and one hobbit."

- Frodo, Ibid.

In the chapter "Flight to the Ford" in Fellowship of the Ring, on their trek to Rivendell, Aragorn and the four hobbits Frodo Baggins, Samwise Gamgee, Meriadoc Brandybuck, and Peregrin Took encountered the three trolls that had been turned to stone seventy-seven years previously, and the hobbits momentarily thought them to be alive.

Portrayal in Adaptations
In the ZX Spectrum adaptation of The Hobbit, which was probably the first licensed adaptation (Wikipedia link, World Of Spectrum link), there were only two trolls featured (probably due to the memory limitations of 8-bit computers), and it is not known which two these were. (Likewise, the game reduced the band of dwarves to just Thorin.)

In the Peter Jackson film The Lord of the Rings: The Fellowship of the Ring (2001), Bilbo recounts the story of his meeting the Trolls to several hobbit-children at his 111th birthday party. In the Extended Version, after Frodo has been stabbed by the Nazgûl Lord and before Arwen arrives to take him to Rivendell, Samwise indicates to the stony trolls above, saying, "Look, Frodo. Bilbo's trolls".

In The Hobbit: An Unexpected Journey, the three trolls are encountered by Bilbo, Fíli and Kíli after having stolen several of the dwarves' ponies. Fíli and Kíli stay back, while Bilbo tries to steal a blade from the trolls to cut the ponies free. When Bilbo is caught accidentally by the trolls, the dwarves charge them to defend him. However, when they threaten to tear Bilbo apart, the dwarves surrender and are put into sacks. Half of the dwarves are put onto the spit, while the others, including Bilbo, are left on the ground. Bilbo spots Gandalf sneaking around, and begins to discuss with the trolls ways of cooking dwarf in order to buy time. As this plan starts to fail, Bilbo claims that the dwarves are carrying parasites to try to put the trolls off of eating them. Then Gandalf appears and breaks a rock that was shielding the trolls from the sunlight, turning them to stone.

The Trolls also make an appearance in the Battle of Middle Earth games in the Weather Top skirmish/multiplayer map. On the far right side by a small stream stand the three petrified trolls.

They were portrayed by William Kircher, Peter Hambleton, and Mark Hadlow (who also played the dwarves Bifur, Gloin and Dori in the film series) by motion capture in the first part of the film.

Portrayal in Video games
The three petrified trolls can also be found in the Trollshaws both in The Lord of the Rings Online game, and in LEGO The Lord of the Rings: The Video Game. They can also be seen scattered throughout Eregion in The Lord of the Rings: The Third Age.