Phineas Nigellus Black was a pure-blood wizard, a member of the esteemed House of Black, and a former Slytherin who served as the Headmaster of Hogwarts School of Witchcraft and Wizardry. Widely regarded as the least popular Headmaster Hogwarts ever had, his legacy is primarily preserved through his magical portrait, which hangs in the Headmaster's office. During the Second Wizarding War, his portrait became an unwilling but crucial means of communication and a source of vital information for Albus Dumbledore, Harry Potter, and the Order of the Phoenix.
Born into the ancient and wealthy Black family, Phineas Nigellus upheld his family's staunch belief in pure-blood supremacy. He attended Hogwarts as a member of Slytherin house and later returned to become its Headmaster. His tenure was characterized by a cynical and often contemptuous attitude towards his students, a sentiment that made him deeply unpopular, even among his own descendants like Sirius Black. His primary role in the narrative occurs long after his death, through his sentient magical portrait. One portrait hangs in the Headmaster's office at Hogwarts, while a duplicate resides at the Black family home, Number Twelve, Grimmauld Place. Phineas Nigellus could travel between these two frames, making him a unique messenger. During the Second Wizarding War, his portrait played a significant, if reluctant, part in the conflict:
Phineas Nigellus's portrait depicts a man with a shrewd, irritable face, astute dark eyes, and a neat, pointed black beard and moustache. He carries himself with an air of arrogant superiority. His personality is defined by his cynicism, sarcasm, and deep-seated prejudice. As a pure-blood supremacist, he held Muggle-borns in utter contempt, frequently referring to Hermione Granger as “the Mudblood” and refusing to take orders from her. He often dismissed the concerns of young people as trivial and referred to students as “dunderheads.” Despite his unpleasant nature, he possessed a reluctant sense of duty to the current Headmaster of Hogwarts, obeying the commands of both Albus Dumbledore and Severus Snape. He also displayed a deep-seated loyalty to Slytherin house and a mournful pride for his family's now-extinct line.
As a former Headmaster of Hogwarts, Phineas Nigellus was undoubtedly a highly accomplished and powerful wizard, proficient in many areas of magic. However, no specific spells or unique magical talents from his lifetime are recorded in the novels. His most notable ability in the series stems from his magical portrait, which was enchanted to be sentient. This enchantment allowed him to hear and see his surroundings, speak with the living, and travel instantaneously to any other portrait of himself, making him an effective, albeit unwilling, spy and messenger.