Hermione Granger: Hermione remains Harry's loyal friend and ally, although she is sometimes critical of his recklessness. She is also struggling with her feelings for Ron and her desire to do well in her sixth year of school.
Ron Weasley: Ron is initially jealous of Harry's newfound success in Potions, but he eventually comes to admire the Half-Blood Prince's methods. He is also dealing with his complex feelings for Hermione and trying to prove himself as a capable wizard in his own right.
Albus Dumbledore: Dumbledore is Harry's wise mentor and guide, although he is sometimes enigmatic and keeps secrets from Harry. He is aware of the growing threat of Voldemort and is trying to prepare Harry for the challenges that lie ahead.
Severus Snape: Snape is the Potions master at Hogwarts and continues to be a complex and ambiguous character. He seems to have a grudge against Harry, but it is also implied that he may have some hidden loyalties.
Ginny Weasley: Ginny has come into her own in her sixth year at Hogwarts and is no longer a shy, retiring figure. She is a talented witch and an important member of the Quidditch team, and she is also Harry's love interest.
Draco Malfoy: Draco is still Harry's main rival at Hogwarts, although he is also conflicted about his loyalties. He is still under pressure from his parents to join Voldemort, but he is also starting to question the cause he is fighting for.