As one of the longest-running sci-fi/fantasy TV shows in America, Supernatural has undeniably developed both its character and fan base. The SPN Family has skyrocketed over the years, with the show's cast and crew regularly connecting with them. With its cult following, well, its family, Supernatural fans regularly discuss new and old characters that either did or didn't affect the show in the long run.
There have been characters (good and bad) that briefly came and went, yet still made a long-term impact on the show. However, it's the villains of Supernatural that left a scar (some literally) on the entire storyline. Only true fans can recognize each villain from the last 15 years.
The Woman In White
From the very first episode all the way to seasons 14 and 15, this villain may have been forgotten over the years. After all, what's a little ghost compared to the bigger forces Sam and Dean fought? Well, although she wasn't one of the biggest baddies, The Woman in White gave the brothers the first glimpse into their strength as a team.
15 years later, she was back in the last episode of Season 14, in Chuck's resurrected army of the undead. Did all viewers even remember her? Well, as said before, only the SPN Family can instantly identify the show's very first villain.
Bloody Mary
Blaming himself for Jessica's death, Sam squared up against this true mirror of a villain, Bloody Mary, in Season 2. She twisted the truth by showing her victims what they were guilty of. The SPN Family certainly knows how self-sacrificial and guilt-ridden the Winchesters always were.
It appeared as though this ghost was put to rest once that gigantic mirror was turned around for Bloody Mary to see her own reflection, as the monster she became. Unfortunately, once Chuck unleashed the actual apocalypse in the last season, fans caught sight of her again in the presence of two innocent teenage girls playing dress-up.
Jenny (The Vampire)
Seeing Jenny return in the finale of Supernatural (let the tears begin) was a shock to fans. Out of all the former monsters, Jenny was once the innocent human that Sam and Dean tried to save, but was turned into a vampire. To recall Season 1, Sam, Dean, and John enter the vamp nest to save any human victim. Once Sam started to untie the girl, she suddenly roared and it was clear that she was a vampire.
Thinking that she was long gone because Sam and Dean rarely left any stone unturned, it was a true surprise for the fandom to see Jenny as a full-grown vamp in the finale. Right before Dean's heartbreaking ending a few moments later, Sam easily chops her head off. So long, Jenny.
Gordon Walker (Hunter Turned Vampire)
Gordon seemed like a potential ally for the Winchesters, especially for Dean in Season 2. Sadly, just like many alliances they formed, this one ended on a truly terrible note. Once a hunter, Gordon's focus on exterminating vampires made sense as it was led by vengeance for his sister's death.
Later on, Gordon revealed his villainy when he tried to kill Sam for his demonic ties. Gordon was later turned into the species he hunted and attempted to get rid of Sam again. Falsely identifying Sam as another monster like him, Gordon planned to kill both Sam and himself as his last "good deeds." Luckily, Sam won the fight, and Gordon was never seen again.
The Djinn
This genie (not the fun, three-wishes kind) was first seen toward the end of Season 2 when Dean was trapped in his own perfect alternate reality. Mary Winchester was back with the boys, Sam was engaged to Jess, and Dean had his dreamy version of a girlfriend. Of course, when Dean realized he wasn't in the real world, he killed the Djinn, only to be hunted by three others in Season 6.
At this point, Dean wasn't actively hunting since his brother sacrificed himself for the Apocalypse (the first one in the show, at least). The Campbell family and Sam helped defeat all the djinns that were dead set on causing Dean's hallucinations, even seeing the famous Yellow-Eyed Demon. The Djinn species reappears through seasons 8, 13, 14, and 15.
Meg
Meg was definitely fascinating. She wasn't just the demon everyone knew her as. She later became the possessed vessel of The Empty: one of the biggest villains of all time on Supernatural, causing some viewers to forget that she was ever anything other than The Empty. Meg was first seen in Season 1 when Sam wanted to leave the family business, then later in Season 2 when she possessed Sam.
Meg later reappeared over the course of seasons 4-9, and 15, finally beginning The Empty's possession of Meg's body to communicate with Castiel. Meg was the villain that wasn't actually forgotten, but her overall changes throughout the show reflect the true wickedness of her fate. It was jarring to see some of her soft sides emerge, primarily when she kissed Castiel in Season 6.
Bela Talbot
This sultry and sly villain had a lot in common with many other bad guys. Bela switches from alliance to the enemy with the Winchesters multiple times. No one would ever forget Dean's reaction when she stole his lottery winnings from the luck of the rabbit's foot in Season 3. She later met the fate she tried to avoid through her demonic allies.
In her attempt to kill Sam and Dean, she was skillfully fooled by the brothers and left for dead. The Hellhounds advanced toward her, sealing her deal that she'd made with a demon years before: to kill her father. While Bela was mainly apparent in Season 3, her fluctuating frenemy relationship with the brothers left a strong mark as she was later referenced in Season 5 by Becky, as having given the colt to Crowley, not Lilith.
Ava Wilson
One of Azazel's "Special Children," Ava was originally an innocent human that befriended Sam for their similar abilities in Season 2. Like Sam, she was later taken as one of the powerful "children," and had been missing for months. Unknown for just how long she was actually evil, Ava surrendered to the demonic powers and murdered some of the people in the group that were miraculously transported to the small town, Cold Oak, in the Season 2 finale.
Yellow Eyes (Azazel) clarified later that this was a fight to the death, a survival of the fittest, for one last powerful human to help Azazel open the Devil's Gate. Sam discovered that she had been feigning her innocent confusion, and she tried to kill him, only to have Jake Talley break her neck and kill her.
Jake Talley
Also part of Azazel's "Special Children" army, Jake was the reason for a multitude of events later on in the show. Stabbing Sam in the back (literally) at the end of Season 2 caused Sam's (first) death and Dean's road of extreme self-sacrifice, making the deal with the crossroads demon. Jake and Sam were initially allies when the others like them were transported to Cold Oak.
Jake, however, gave in and played into Azazel's intentions. His mental abilities were transformed into demonic, stronger powers, serving as an assistant to Azazel, but was killed by Sam in the end. It was because of Jake that Dean sacrificed everything for his brother, and was sent to Hell one year later.
Alastair
He may have been forgotten over time, but this torturer of Hell was Dean's ingrained nightmare. Referring to him as one of his "students," Alastair scarred Dean for awhile. In Season 4, Dean tearfully admitted to Sam how he either had to be tortured or become the torturer on the souls in Hell.
Alastair is mentioned later on in Season 6 by Meg, who was also a "student" under him in Hell for violent lessons, and in Season 15 by the demon, Belphegor. Alastair is the buried, but not ignored, villain that haunted Dean's memory. Even with Chuck's (can't forget about him) label of Dean in Season 15 as "the ultimate killer," Alastair was one of the earliest villains to instill that false image of Dean as a killer.