Orion Black is the father of Sirius and Regulus; he heavily fortified the family home (likely inherited by his wife, also a Black) at number twelve Grimmauld Place, London.
Son of Arcturus and Melania (MacMillan) Black (BFT).
One older sister: Lucretia (1915-1992).
Married his second cousin Walburga Black (BFT).
Heavily fortified Grimmauld Place and made it unplottable to either Muggles or Wizards.
Other canon notes and references
Orion Black and his wife Walburga were cousins, both descendants of Phineas Nigellus Black (also confirmed by BFT). This explains why she refers to the House of Black as the "house of my fathers" (OP4).
When Harry takes the Astronomy part of his O.W.L. exam, he has to draw the constellation Orion (OP31). This happens just before his vision that Sirius Black (Orion Black's son) is being tortured at the Department of Mysteries.
Orion is one of the brightest and most recognizable constellations in the night sky, thought to form the shape of a giant hunter with arms, legs, and a bright belt of stars. The constellations Canis major and Canis minor (big dog and little dog) are his hunting companions.