Question: Which character in Harry Potter and the Prisoner of Azkaban helped Harry rescue Hermione Granger from a troll?

full_context: Document 1: Ron Weasley: Ronald Bilius "Ron" Weasley is a fictional character in J. K. Rowling's "Harry Potter" series. His first appearance was in the first book of the series, "Harry Potter and the Philosopher's Stone" as the best friend of Harry Potter and Hermione Granger. He is a member of the Weasley family, a pure blood family, who reside in "The Burrow" outside Ottery St. Catchpole. Along with Harry and Hermione, he is a member of the Gryffindor house. Ron is present in most of the action throughout the series.
Document 2: Fantastic Beasts and Where to Find Them: Fantastic Beasts and Where to Find Them is a 2001 book written by British author J. K. Rowling (under the pen name of the fictitious author Newt Scamander) about the magical creatures in the "Harry Potter" universe. The original version purports to be Harry Potter's copy of the textbook of the same name mentioned in "Harry Potter and the Philosopher's Stone" (or "Harry Potter and the Sorcerer's Stone" in the US), the first novel of the "Harry Potter" series. It includes several notes inside it supposedly handwritten by Harry, Ron Weasley, and Hermione Granger, detailing their own experiences with some of the beasts described, and including in-jokes relating to the original series.
Document 3: Hogwarts staff: The following fictional characters are staff members and denizens of Hogwarts in the "Harry Potter" books written by J. K. Rowling.
Document 4: Harry Potter and the Half-Blood Prince: Harry Potter and the Half-Blood Prince is the sixth and penultimate novel in the "Harry Potter" series, written by British author J. K. Rowling. Set during protagonist Harry Potter's sixth year at Hogwarts, the novel explores the past of Harry's nemesis, Lord Voldemort, and Harry's preparations for the final battle against Voldemort alongside his headmaster and mentor Albus Dumbledore.
Document 5: Harry Potter and the Chamber of Secrets: Harry Potter and the Chamber of Secrets is the second novel in the "Harry Potter" series, written by J. K. Rowling. The plot follows Harry's second year at Hogwarts School of Witchcraft and Wizardry, during which a series of messages on the walls of the school's corridors warn that the "Chamber of Secrets" has been opened and that the "heir of Slytherin" would kill all pupils who do not come from all-magical families. These threats are found after attacks which leave residents of the school "petrified" (frozen like stone). Throughout the year, Harry and his friends Ron and Hermione investigate the attacks.
Document 6: Harry Potter and the Prisoner of Azkaban: Harry Potter and the Prisoner of Azkaban is the third novel in the "Harry Potter" series, written by J. K. Rowling. The book follows Harry Potter, a young wizard, in his third year at Hogwarts School of Witchcraft and Wizardry. Along with friends Ronald Weasley and Hermione Granger, Harry investigates Sirius Black, an escaped prisoner from Azkaban who they believe is one of Lord Voldemort's old allies.
Document 7: Harry Potter and the Prisoner of Azkaban (film): Harry Potter and the Prisoner of Azkaban is a 2004 British-American fantasy film directed by Alfonso Cuarón and distributed by Warner Bros. Pictures. It is based on the novel of the same name by J. K. Rowling. The film, which is the third instalment in the "Harry Potter" film series, was written by Steve Kloves and produced by Chris Columbus (director of the first two instalments), David Heyman, and Mark Radcliffe. The story follows Harry Potter's third year at Hogwarts as he is informed that a prisoner named Sirius Black has escaped from Azkaban intending to kill him.
Document 8: Harry Potter and the Philosopher's Stone: Harry Potter and the Philosopher's Stone is the first novel in the "Harry Potter" series and J. K. Rowling's debut novel, first published in 1997 by Bloomsbury. It was published in the United States as Harry Potter and the Sorcerer's Stone by Scholastic Corporation in 1998. The plot follows Harry Potter, a young wizard who discovers his magical heritage as he makes close friends and a few enemies in his first year at the Hogwarts School of Witchcraft and Wizardry. With the help of his friends, Harry faces an attempted comeback by the dark wizard Lord Voldemort, who killed Harry's parents, but failed to kill Harry when he was just 15 months old.
Document 9: Harry Potter and the Goblet of Fire: Harry Potter and the Goblet of Fire is the fourth novel in the "Harry Potter" series, written by British author J. K. Rowling. It follows Harry Potter, a wizard in his fourth year at Hogwarts School of Witchcraft and Wizardry and the mystery surrounding the entry of Harry's name into the Triwizard Tournament, in which he is forced to compete.
Document 10: Harry Potter and the Philosopher's Stone (film): Harry Potter and the Philosopher's Stone (released in some countries as Harry Potter and the Sorcerer's Stone) is a 2001 British-American fantasy film directed by Chris Columbus and distributed by Warner Bros. Pictures. It is based on the novel of the same name by J. K. Rowling. The film is the first instalment in the long-running "Harry Potter" film series, and was written by Steve Kloves and produced by David Heyman. Its story follows Harry Potter's first year at Hogwarts School of Witchcraft and Wizardry as he discovers that he is a famous wizard and begins his education. The film stars Daniel Radcliffe as Harry Potter, with Rupert Grint as Ron Weasley, and Emma Watson as Hermione Granger.
Document 11: Harry Potter (character): Harry James Potter is the title character and protagonist of J. K. Rowling's "Harry Potter" series. The majority of the books' plot covers seven years in the life of the orphan Potter, who, on his eleventh birthday, learns he is a wizard. Thus, he attends Hogwarts School of Witchcraft and Wizardry to practise magic under the guidance of the kindly headmaster Albus Dumbledore and other school professors. Harry also discovers that he is already famous throughout the novel's magical community, and that his fate is tied with that of Lord Voldemort, the internationally feared Dark Wizard and murderer of his parents, Lily and James.
Document 12: Harry Potter and the Philosopher's Stone: Harry Potter and the Philosopher's Stone is the first novel in the "Harry Potter" series and J. K. Rowling's debut novel, first published in 1997 by Bloomsbury. It was published in the United States as Harry Potter and the Sorcerer's Stone by Scholastic Corporation in 1998. The plot follows Harry Potter, a young wizard who discovers his magical heritage as he makes close friends and a few enemies in his first year at the Hogwarts School of Witchcraft and Wizardry. With the help of his friends, Harry faces an attempted comeback by the dark wizard Lord Voldemort, who killed Harry's parents, but failed to kill Harry when he was just 15 months old.
Document 13: Dumbledore's Army: Dumbledore's Army (or D.A. for short) is a fictional student organisation in J. K. Rowling's "Harry Potter" series that is founded by the main characters, Harry Potter, Ron Weasley and Hermione Granger, to stand up against the regime of Hogwarts High Inquisitor Dolores Umbridge, as well as to learn practical Defence Against the Dark Arts. It was founded in the fifth book, "Harry Potter and the Order of the Phoenix". Cho Chang conceives of the abbreviation "D.A." and Ginny Weasley conceives of the name "Dumbledore's Army".
Document 14: Emma Watson: Emma Charlotte Duerre Watson (born 15 April 1990) is a British actress, model, and activist. Born in Paris and brought up in Oxfordshire, Watson attended the Dragon School and trained as an actress at the Oxford branch of Stagecoach Theatre Arts. She rose to prominence after landing her first professional acting role as Hermione Granger in the "Harry Potter" film series, having acted only in school plays previously. Watson appeared in all eight "Harry Potter" films from 2001 to 2011, earning worldwide fame, critical accolades, and around $60 million.
Document 15: Hermione Granger: Hermione Jean Granger ( ) is a fictional character in J. K. Rowling's "Harry Potter" series. She first appears in "Harry Potter and the Philosopher's Stone", as a new student on her way to Hogwarts. After Harry and Ron save her from a mountain troll in the girls' toilets, she becomes best friends with them and often uses her quick wit, deft recall, and encyclopaedic knowledge to help them. Rowling has stated that Hermione resembles herself at a younger age, with her insecurity and fear of failure.
ground_truth: Ronald Weasley