Mary Winchester is mother of Sam and Dean, the wife of John Winchester, and the aunt of Claire and Jacob Winchester.
Mary born to a family of hunters. She later marries John Winchester and gives birth to Dean and Sam. After Sam was born a yellow eyed demon killed her and John later went out for revenge. Mary never got to meet her nephew and niece Jacob and Claire as they were born in 1995 years after her death and they only know about her because Sam and Dean told them what she looked like and this made Jacob angry or as he describes madder then a son of a bitch. Mary is later resurrected by Castiel who he wanted to meet her nephew and niece.