Sirius Black III

Sirius Orion Black (born 3 November, 1959) is an English pure-blood wizard and the eldest son and child of Orion and Walburga Black. Sirius disagreed with his family's beliefs of blood purity even though he was the heir to the House of Black. When he was little, he was close friends with his cousins, especially Andromeda, who also didn't agree with the family's beliefs of blood purity. 
Sirius attended Hogwarts from 1971–1978 and was sorted into Gryffindor House, defying the Black family tradition of being sorted into Slytherin (though all his children ended up being sorted into Slytherin; his father called it 'a small hiccup in the system'). He met three good friends at Hogwarts- James Potter, Remus Lupin, and Peter Pettigrew. They were referred to as the Marauders. Along with James and Peter, Sirius became an animagus in his fifth year in order to help their friend Remus, who was a werewolf. Sirius took the form of a black dog. In their sixth year, the Marauders developed a map that showed anyone on Hogwarts grounds, which later became known as 'The Marauders' Map'. 
After he graduated, he was notified by his parents that he was betrothed to Margaret Black (née Macmillan), a pure-blood Hufflepuff girl from the House of Macmillan who attended school at the same time as him. Sirius was very surprised at this as they had never mentioned marriage. Margaret later revealed to him that they had only made the deal a year before their graduation. Sirius and Margaret did end up falling in love with each other and had three children: Ganymede Black in July 1979, Io Black in June 1980, and Vega Black III in October 1985. Although his wife and his grandmother have the same surname, their last common ancestor traces 5 generations back. 
After his marriage with Margaret, they moved into Black Manor, where his grandparents lived. He didn't want to live with his parents at 12 Grimmauld Place. He only later moved there after both his parents passed away.