In ‘Harry Potter and the Half-Blood Prince,’ one of the most significant deaths is that of Albus Dumbledore. He is killed by Severus Snape atop Hogwarts as part of a pre-arranged plan with Dumbledore himself. This event is crucial as it not only impacts Harry and his friends but also sets the stage for the final confrontation with Voldemort.
Additionally, there are other deaths that resonate throughout the story, such as that of Fenrir Greyback’s victims, showcasing the ongoing danger posed by Voldemort’s followers. However, Dumbledore’s death is the emotional core of the book, representing the loss of wisdom and guidance for Harry and the fight against the dark forces.