Cygnus Black, the great-grandson of Phineas Nigellus Black, is the father of Bellatrix, Andromeda, and Narcissa Black. He is the maternal uncle to Sirius and Regulus. Cygnus was married to to Druella Rosier.
Cgynus Black is a part of the large and prestigious wizarding family, the Black family.
'Cygnus' = a male swan (Latin), the name of a constellation, which is fitting with the Black predilection for astronomical names. In Greek mythology, 'Cycnus' was the Musician-king of the Ligurians who was turned into a swan (EM).
A little math reveals that Cygnus fathered his first child at the age of 13. Started early, did Cygnus Black. Presumably this is an error on the Black Family Tree, but until Rowling corrects it, this is the date we have.
From the Web
Cygnus from Encyclopedia Mythica