SPOILER ALERT!
We have seen both the Winchester man as well as some people without who they'd be nothing. However, there is no denying that without a certain two people, these brothers never would have existed. A lot of their complicated history is because the boys lost their mother at a young age, wich is why today will focus on Mary Winchester as portrayed by Samantha Smith.
Mary was born into a Hunter's family as Mary Campbell. By an accident, caused by her future son Dean Winchester, a young Mary Campbell suddenly grabs the attention of the demon Azazel. He kills her parents and her current boyfriend: John Winchester. Mary makes a deal with Azazel to resurrect John by allowing him entrance at her house ten years later. She eventually married John Winchester and gave birth to two sons in the ten years that came after.
When Sam was only six months olds, Mary discovers Azazel standing over her baby boy, feeding him demonblood. As she confronted him, Azazel killed her and all of her friends. As a result, John Winchester and his sons started to hunt down Mary's murderer, becoming Hunters in the process. Eventually, 33 years after she had been killed, Mary is resurrected by the Darkness as a gift for making her and God reconcile. It is up to Dean to explain everything that has been going on in these years.
Even in death, Mary has always been ready to protect her family and she was devistated to learn that John had died when she had only been a spirit. After her resurrection, she keeps protecting people and even sacrificed herself to trap Lucifer in the Apocalypse. She is a true devoted wife and mother, but also a totally badass Hunter!
As important as Mary Winchester is to the Supernatural universe, that little is known about actress Samantha Smith. Samantha started her career as a teenage model. During her college years, she started doing commercials to help her pay for UCLA. Eventually one of these commercials aired during the Super Bowl, which was the start of her acting career.
While Supernatural is the only tv series where Samantha starred regularly, she did make a name for herself on the big screen as Sarah Lennox in the Transformers and Juliet in The Truth about Juliet. Apart from that, she also guessed starred in famous tv series like Criminal Minds, Friends, NCIS: LA and the Mentalist.
Even less is known about her personal life. All we know is that Samantha is married and has a son with her partner, though the names of her partner and her son are unknown to us.