Phineas Nigellus Black

Phineas Nigellus Black (1847–1926), more commonly known as Phineas Nigellus, is the great-great-grandfather of Sirius Black and said to be the least popular headmaster Hogwarts ever had (though it is possible Dolores Umbridge has since usurped this title). He had an older brother, Sirius Black (who died in childhood), and two younger sisters, Elladora Black (who started the family tradition of beheading aged house-elves) and Isla (Black) Hitchens (who was disowned for marrying Bob Hitchens, either a Muggle or a Muggle-born wizard). He was married to Ursula (Flint) Black, and had five children: Sirius Black, Phineas Black (disowned for supporting Muggle rights), Cygnus Black, Belvina (Black) Burke, and Arcturus Black. Harry Potter's godfather Sirius Black is descended from Phineas Nigellus through two of his sons, Sirius and Cygnus.

Phineas' portrait hangs in the headmaster's office along with the portraits of the other ex-headmasters and headmistresses. Like the other portraits in the headmaster's office, the painting of Phineas helps the current headmaster. He does not seem to enjoy doing this. Albus Dumbledore addresses the portrait as if it were Nigellus himself.

He does not get along well with his great-great-grandson, young people or most people for that matter; however, he did seem somewhat upset to find out Sirius, the last male Black, was dead, for either purely dynastic or emotional reasons. He, along with Ginny Weasley, is unusual in being a character who openly criticises Harry Potter's often rash behaviour in Order of the Phoenix.

A second portrait of Phineas hangs in the Black family home at 12 Grimmauld Place, and like other characters in portraits in the wizarding world, Phineas can travel between his portraits. In Order of the Phoenix, Harry uses the bedroom where Phineas' portrait is hanging, and Phineas takes him messages from Albus Dumbledore. His voice can sometimes still be heard coming from the frame when he is not in it, making sarcastic comments.

Name etymology
The Black patriarch's middle name, "Nigellus", means "little Black", in Latin.

In the Bible, Phinehas, grandson of Aaron, is an extremely controversial high priest who murders two persons because they were having sex on the steps of the Tabernacle (the building containing the Holy Ark), and because one is Jewish and the other is not. His example has been used to justify attacks on interracial couples over the centuries. The Hebrew name Phinehas is also believed by many to be derived from the Egyptian name Pa-Nehasy, which means "The Nubian," or perhaps even "The Black Man."

In some versions of the myth of Perseus, Phineus is a former lover of Andromeda.

"Nigellus" is also the Latin form of the British name Nigel, itself originally of Latin origin.

It was initially believed by readers that Nigellus was his surname, and that it was probably anglicised to "Black" after his time. However, it was stated in "Harry Potter and the Half-Blood Prince" that his full name is Phineas Nigellus Black.

Phineas Nigellus and his wife, Ursula Flint, are the oldest known ancestors of the "Ancient and Noble House of Black". This family is a very large one, having ties to many other prominent magic families in the Harry Potter series.

Characters that have appeared in the books who are known to be descended from Phineas Nigellus include: Sirius Black, Draco Malfoy, Narcissa Malfoy, Bellatrix Lestrange and Nymphadora Tonks.

Additionally, the family tree suggests that Phineas may have descendants in the Potter, Weasley and Longbottom clans, as well as in the Crouch, Prewett and Burke families. Furthermore, many other familiar surnames occur in the tree among the Blacks' spouses, tying the family to other (likely pure-blooded) Wizarding families. For example, Sirius Black's female ancestors include an Ursula Flint, a Violetta Bulstrode, a Melania Macmillan, and an Irma Crabbe.

Hence, though Phineas's line might be extinct in name, he actually still has descendants whose family names just aren't "Black". It is possible that many, most or even all pure-bloods and many half-bloods are related to Phineas in one way or another.