Cho Chang
Background
Cho Chang is a witch from house Ravenclaw and student at Hogwarts School of Witchcraft and Wizardry. Her mother works at the Ministry of Magic.
During the events of Harry Potter and the Goblet of Fire (2005) played by Katie Leung
On the Hogwarts Express, Food Trolley Lady asks if anyone wants something. As Harry Potter is looking at the trolley, Cho walks up and buys something from the trolley and she and Harry smile at each other. Padma Patil and Parvati Patil say hello to Harry as they walk by, but he focuses his attention on Cho. Harry eventually asks Cho to the Yule Ball, but she apologizes and tells him she already said she would go with someone else. On the day of the ball, Cedric Diggory goes with Cho. During the second challenge of the Triwizard Tournament, each challenger must collect a loved one from the Black Lake. Cedric frees Cho and ties with Harry for second place.
During the events of Harry Potter and the Order of the Phoenix (2007) played by Katie Leung
Harry sees Cho Chang, who smiles at him, and Neville, says hello to Harry, Hermione and Ron. During the Hogwarts banquet, Albus Dumbledore welcomes back Professor Grubbly-Plank as the Care of Magical Creatures while Hagrid is away. He then introduces Dolores Umbridge as the new Defense Against the Dark Arts teacher. Dolores interrupts Dumbledore and tells the students that the Ministry of Magic is very concerned about their education. Dolores and Professor McGonagall have an argument about Harry's punishment and Dolores declares that things at Hogwarts are worse than the Ministry thought.
Hermione Granger organizes a meeting with some of the other students at Hog's Head, where Barman works. Somewhat Doubtful Boy wonders why they need to be taught how to combat the dark arts and Slightly Creepy Boy asks Harry to describe more of what happened when Cedric was killed. Nigel asks if Voldemort is really back, and Harry tells everyone he is. They then form a group called Dumbledore's Army. Dumbledore's Army, which consists of Harry, Hermione, Ron Weasley, Fred Weasley, George Weasley, Ginny Weasley, Neville Longbottom, Cho, Nigel, Dean Thomas, Padma, Parvati, Somewhat Doubtful Boy, Slightly Creepy Boy and others, uses the Room of Requirement to train. Dumbledore's Army has one last lesson before Christmas break and Cho stays after class and she and Harry kiss under mistletoe. During one of their training sessions, they are caught by Dolores, Mr Filch and the student members of the inquisitors. Percy Weasley drags Harry and Cho, who told the location of the training session, to the meeting with Cornelius Fudge, Kingsley Shacklebolt, Dawlish and Dolores in Dumbledore's office. They accuse Dumbledore of forming an army to revolt against the Ministry. Fudge orders Kingsley and Dawlish to take Dumbledore to Azkaban and Dumbledore escapes with the help of Fawkes.
During the events of Harry Potter and the Half-Blood Prince (2009) played by Katie Leung
Dumbledore introduces the students to Professor Horace Slughorn and tells the students that dark forces are trying to penetrate Hogwarts.