"You know, this is precisely why I loathed being a teacher! Young people are so infernally convinced that they are right about everything."
-- Phineas Nigellus (OP23)
Great-great-grandfather of Sirius Black, who has been known to refer to him as the least-popular Headmaster Hogwarts has ever had (OP6).
Phineas' portrait hangs in the Headmaster's office along with those of other previous Headmasters, and he rather grudgingly helps Dumbledore when pressed. His portrait also hangs in number twelve Grimmauld Place (OP37); he and Sirius did not get along well.
Phineas is a snide, sarcastic fellow. He has little patience for the feelings and the problems of others, particularly young people, whom he finds tedious and self-absorbed (OP23).
Phineas helped Hogwarts Headmaster Snape keep a track of the movements of Harry, Ron, and Hemione when they were on the run from the Death Eaters because Hermione had placed his portrait from Grimmauld Place into her beaded bag (DH12, DH15).
Parentage: not given (BFT). Phineas' surname was confirmed as 'Black' in HBP13.
3 Siblings: Sirius, Elladora, and Isla (who was disowned for marrying a Muggle) (BFT).
Married to Ursula Flint (BFT)
- Sirius (1877-1952) husband of Hesper Gamp (BFT)
- Phineas (disowned, dates unknown) (BFT)
- Arcturus (1884-1959) (BFT)
- Belvina (1886-1962) (BFT)
- Cygnus (1889-1943) husband of Violetta Bulstrode (BFT)
Great-great-grandfather of Sirius Black. According to the Black Family Tree that Jo drew, Phineas is also an ancestor of Narcissa (Black) Malfoy, Molly (Prewett) Weasley and Arthur Weasley (BFT and my notes).
Possible name origins: 'Phineas' is an English variant of 'Phinehas,' a name from the Bible. 'Phinehas' probably means "Nubian," though some believe it means "serpent's mouth" in Hebrew (BtN). Among the things Phinehas in the Bible is known for is being so strongly opposed to intermarriage between Israelites and people of other groups that he personally killed an Israelite-Midianite couple (source: Wikipedia).
In Greek mythology, Phineus was "a king of Thrace and a prophet. Because he prophesied too truly, revealing too much of the gods' truth to humans, Zeus blinded him and set the Harpies to plague him." Phineus later helps the Argonauts by telling them how to get past one of their hazards. (EM)
Phineas' surname was confirmed as 'Black' in HBP13. One possible explanation for the Latinization of his surname ('Black' = 'Nigellus') is that during the 16th and 17th centuries it was common for educated persons to Latinize their names. Perhaps some day we will know the names of Phineas's ancestors. Were they 'Nigellus" or 'Black?'
Interestingly, Phineas' dates mean that (until his death, at least) he was a near contemporary of Albus Dumbledore.
JKR on Wizard Portraits
Question: All the paintings we have seen at Hogwarts are of dead people. They seem to be living through their portraits. How is this so? If there was a painting of Harry’s parents, would he be able to obtain advice from them?
JKR: That is a very good question. They are all of dead people; they are not as fully realised as ghosts, as you have probably noticed. The place where you see them really talk is in Dumbledore’s office, primarily; the idea is that the previous headmasters and headmistresses leave behind a faint imprint of themselves. They leave their aura, almost, in the office and they can give some counsel to the present occupant, but it is not like being a ghost. They repeat catchphrases, almost. The portrait of Sirius’ mother is not a very 3D personality; she is not very fully realised. She repeats catchphrases that she had when she was alive. If Harry had a portrait of his parents it would not help him a great deal. If he could meet them as ghosts, that would be a much more meaningful interaction, but as Nick explained at the end of Phoenix—I am straying into dangerous territory, but I think you probably know what he explained—there are some people who would not come back as ghosts because they are unafraid, or less afraid, of death.