What was the surname of Isaac Newton's stepfather?

Isaac Newton’s stepfather’s surname was Smith. Newton’s mother, Hannah Ayscough, married the Reverend Barnabas Smith in 1646, when Isaac was about three years old.

Because Barnabas Smith became Newton’s stepfather rather than his biological father, the name can be confused with Newton’s own family surname. Newton’s father, also named Isaac Newton, had died several months before Isaac was born. After Hannah’s remarriage, young Isaac remained at Woolsthorpe for a time in the care of his maternal grandmother, Margery Ayscough, while his mother lived with Barnabas Smith at North Witham.

Newton apparently resented the marriage and his separation from his mother. A list of youthful sins that he later wrote included a threat to burn his parents and their house, often interpreted as evidence of his anger toward the household. Barnabas Smith died in 1653, after which Hannah returned to Woolsthorpe with her children from the second marriage. Newton therefore spent only part of his childhood in direct proximity to his stepfather, but Smith’s role is an important detail in accounts of Newton’s early life.