Viktor Krum is a fictional character in J.K. Rowling’s Harry Potter series. He is a skilled Seeker for the Bulgarian National Quidditch team and a student of Durmstrang Institute. Throughout the series, Krum plays a pivotal role in the Triwizard Tournament and in the fight against Voldemort and his Death Eaters. Here is a brief overview of what happens to Viktor Krum in the Harry Potter series:

In Harry Potter and the Goblet of Fire, Viktor Krum is introduced as one of the champions of the Triwizard Tournament. He is a skilled Quidditch player and is known for his prowess as a Seeker. During the tournament, Krum faces several challenges, including the first task, where he must retrieve a golden egg from a dragon. Despite suffering from a burn injury, Krum completes the task successfully. In the second task, Krum dives into the Black Lake to rescue his captive partner, Hermione Granger, and is the first to return to the surface.
During the Yule Ball, Krum asks Hermione to be his date, and they dance together. It is clear that Krum has developed feelings for Hermione, although she seems somewhat taken aback by his sudden attention. In the final task of the tournament, Krum is placed under the Imperius Curse by one of the Death Eaters and attacks Cedric Diggory. However, he is quickly brought back to his senses by Harry Potter, and the two of them work together to solve the final challenge.
In Harry Potter and the Deathly Hallows, Viktor Krum is seen briefly when he is captured and held hostage by Death Eaters. He is forced to wear a cursed necklace that affects his mind and behavior, causing him to become aggressive and hostile. However, he is eventually freed by Harry, Ron, and Hermione, who have infiltrated the Ministry of Magic to steal one of Voldemort’s Horcruxes.
After the Battle of Hogwarts, Krum returns to Bulgaria and continues to play Quidditch. He becomes the captain of the Bulgarian National team and leads them to victory in the Quidditch World Cup. He also maintains his friendship with Hermione, despite the fact that she eventually marries Ron Weasley.
In the epilogue of Harry Potter and the Deathly Hallows, which takes place nineteen years later, Krum is briefly mentioned as having attended the wedding of Harry Potter and Ginny Weasley. He is described as having aged gracefully and still being regarded as one of the greatest Seekers of all time.
Overall, Viktor Krum plays a significant role in the Harry Potter series, particularly in the Triwizard Tournament. He is a skilled and determined competitor, but also demonstrates loyalty and bravery when he is placed under the Imperius Curse. Although his romantic interest in Hermione is not reciprocated, he remains a loyal friend to her and continues to play Quidditch at the highest level. In the end, he is remembered as a talented athlete and a hero of the Wizarding World.