Cygnus Black I (1829-1851) was the eldest son and second child of Licorus Black and Magenta Tripe as well as the brother of Misapinoa Black and Arcturus Black I. He is the father of Sirius Black I, Phineas Nigellus Black (Headmaster of Hogwarts), Elladora Black and Iola Black.
Cygnus was born in 1829 as the middle child in the powerful and rich Black Family in London. He started his education at Hogwarts in 1840 and ended it in 1847. He was sorted into Slytherin House.
Somehow and very controversally he and Ella Max married while they were still at Hogwarts and had Sirius. Ella didn't finish her education because of this. They had three more children. Cygnus tragically died during his wife's fourth pregnancy while his children were 6, 4 and 1 year old.
The youngest of his children, Iola, was disowned in 1875 for marrying muggle Robert Hitchens.
Cygnus was a difficult man with lots of tantrums.