Early life
Blaise Zabini was the son of a famously beautiful witch who had been widowed seven times over by 1996. Each husband's death occurred both under suspicious circumstances and left the already wealthy Ms. Zabini and her son richer. It is unknown if Blaise's biological father was one of the seven late husbands. Blaise is more than likely a pure-blood wizard, as he disliked "blood traitors" and people who associated with Muggle-borns. He was incredibly vain and did not befriend Muggles or Muggle-borns.
Hogwarts years (1991-1998)
Early years
In 1991, Blaise started his education at Hogwarts School of Witchcraft and Wizardry and was Sorted into Slytherin House. Due to Blaise's reserved nature, he kept to himself most of the time and did not really make friends with other Slytherins, nor other students in his year — though this may have been because he was prejudiced against Muggle-borns and "blood traitors." To a small extent, Blaise seemed to get along with Draco Malfoy and Pansy Parkinson — he was able to sit with them on the train journey to Hogwarts — but other than that, he was not mentioned to be hanging around that group.
Sixth year
Pansy Parkinson: "Even you think she's good looking, don't you, Blaise, and we all know how hard you are to please!"
Blaise: "I wouldn't touch a filthy blood traitor like her whatever she looked like."
— Pansy and Blaise discussing Ginny Weasley