Supernatural premiered 14 years ago, with its pilot episode setting up the world of the Winchesters with the brothers' tragic backstory: When Sam was a baby, his mother, Mary Winchester, was killed by a yellow-eyed demon in his nursery, and John Winchester, the brothers' father, had been on a quest for revenge ever since.
In the years to come, the Winchesters would face off against numerous creeps and creatures. Sam and Dean no longer need to consult John Winchester's journal of monsters, because they now have more resources and experience than he did. However, the pilot episode kicked off this monster roster with the Woman in White.
The Woman in White is a type of spirit that takes the form of a beautiful woman (it helps that the person in real life was beautiful as well). In her life, her husband deceived her, causing her to have a mental break, kill her children and then die from suicide. So, in her afterlife, she uses her looks to kidnap men, and then she takes her true ghastly form to kill them.
Dean fetches Sam -- who's got a good life with a lovely girlfriend and grand plans of law school -- because their dad has gone missing. They haven't seen each other in a couple of years, as Sam wanted to break free of the hunting lifestyle. Sam begrudgingly joins Dean to find their dad, who went missing after pursuing the case of missing men from Centennial Highway. The spirit responsible for the missing men is the Woman in White.
The Woman in White is the catalyst for bringing the two Winchester brothers together, as the rest of the first season has them hunting while trying to find their dad. Additionally, Sam wants to avenge the death of his girlfriend, who died in the same gruesome way as his mother -- pinned to the ceiling bleeding from the gut and then set aflame.
Compared to the complicated relationships between the creatures of Hell and the creatures of Heaven that would come in the later seasons, the idea of the Woman in White is simple. The concept is something that immediately makes sense to audiences -- no one is going to question a vengeful spirit -- and she's just scary enough to appeal to a large swatch of audiences. However, unlike Bloody Mary, who was also featured in the first season, the Woman in White wasn't very memorable until we were reminded of her in the Season 14 finale.
The trailer for Supernatural's final season namedrops the Woman in White specifically; she's one of the many creatures that are brought back. This certainly raises the stakes for the Winchesters since they've spent the last 15 years putting these supernatural beings away, and now the Woman in White has had some time to get even angrier at these two men.
The callback to the Woman in White makes us remember Supernatural's roots. First, she reminds us of another woman in white we were introduced to in the pilot episode: Mary Winchester was wearing a white nightgown when she died. And so much has happened since then that some of us need to be reminded of how it all started. For example, remember how Sam had psychic abilities and a special connection to the demon that killed his mother? Remember how Dean's first save from death was by a reaper being controlled by a preacher’s wife? And that's just Season 1 examples. With 14 seasons of mythology to reference in the final season, it's significant that the show references how "the road so far" began in the first place.
Considering that the boys have had bad luck with women -- the life of a hunter isn't conducive to having a longterm relationship -- the Woman in White coming back to seek her revenge is even sweeter. In general, even their friendships with women don't last that long, with the exception of Rowena. Additionally, many women have died because of their connection to the boys over the years: Ellen and her daughter Jo, Charlie, and Mary Winchester (twice!), to name a few.
It's the Woman in White that got Sam to join Dean to hunt together and try to find their dad. Therefore, it's fitting that she has a role, however small, in the final season.
Returning Thursday, Oct. 10, at 8 p.m. ET/PT on The CW for its final season, Supernatural stars Jensen Ackles, Jared Padalecki, Misha Collins and Alexander Calvert.