Cedric Diggory was the son of Amos Diggory and his wife. He started attending Hogwarts School of Witchcraft and Wizardry and was sorted into Hufflepuff. During his time at the school, he was a prefect, and captained the Hufflepuff Quidditch team, playing as Seeker. In his seventh year, Cedric put his name forward to compete in the Triwizard Tournament. He was selected as the Hogwarts Triwizard Champion, and, although overshadowed in the press by the entry of Harry Potter, Cedric enjoyed almost overwhelming support from the student body, and, after the first two tasks, tied with Harry for first place. In the third task, Harry and Cedric were transported to Little Hangleton Graveyard when they touched the Triwizard Cup, which had been secretly turned into a portkey. There, Cedric was murdered by Wormtail on Voldemort's orders. When Harry and Voldemort's wands connected in Priori Incantantem, Cedric's ghost asked Harry to return his body to his father.
In the video game, Cedric is not killed by Wormtail, but falls apart when he and Harry run to the portkey and Voldemort shoots a killing curse at them. After Harry returns to Hogwarts with Cedric's pieces Professor Dumbledore hands Amos Diggory a paper on how to construct a minifigure, so Cedric was most likely reconstructed (but it is not shown).
However, in the sequel, it is implied that Cedric is still dead.