With 15 seasons of following the beloved Winchester brothers in their quest to save people and hunt demons, Supernatural is a show that has seen a lot of characters. Season 1 alone introduces the audience to the brothers, their dad, Bobby, Mary, and Azazel, among others. These are some of the best and most vital characters of the show.
However, there is no doubt the majority of the show's beloved, iconic characters come after its first season. Villains with an arc that led them to be heroes, side characters who became integral to the show, and an angel that became a tertiary main character are just some of the many, many fantastic characters who debuted after "Devil's Trap."
Chuck
Chuck, aka Carver Edlund, aka God, was in the Kripke-era of Supernatural. He was a funny recurring side character, a prophet who later revealed himself to everyone as God.
Chuck was introduced in season 4 as Carver Edlund before mysteriously leaving in season 5 and returning as God five seasons later. The character has some fantastic moments throughout the show as he goes from a quirky ally with immense power to the big bad of the final season who is throwing a tantrum and destroying worlds.
Jody Mills
The Wayward sisters are some of Sam and Dean's most beloved friends, and the longest-standing member of this group of women is Sherrif Jody Mills.
Debuting in season 5 as Sam and Dean investigate the zombies around her small town, Jody ended up having to kill her own zombie son before being a fantastic ally to the brothers, showing up in every season after that, and always being a welcome sight for fans.
Charlie Bradbury
Another character who was adored by fans and Winchesters alike is Charlie Bradbury, a character who, despite being so great, got one of the most undeserving endings in the entire series.
Charlie debuted in season 7 as an employee of Dick Roman's company Richard Roman Enterprises and formed a close bond with the boys for the next three seasons before being murdered in a motel bathtub. The apocalypse world version of the character did appear in the show, but she was not quite the same.
Gabriel
First introduced as the Trickster, one of the best, funniest villains in the Kripke-era of Supernatural, this character later revealed himself to be none other than one of the four main worlds' archangels, Gabriel.
The youngest of the archangels debuted in season 2 as the Trickster, a persona he kept up until season 5's incredible episode "Changing Channels." Gabriel "died" and returned a couple of times before dying for real in season 13, meeting his end at the hands of alternate Michael.
Ellen & Jo Harvelle (& Ash)
Alongside Bobby's junkyard and the Impala, the Harvelle's Roadhouse was one of the only places Sam and Dean could take sanctuary in, and it was also the home of three of their most important friends in the early seasons.
Ellen and Jo Harvelle, as well as the hilarious Ash, debuted in season 2 to help the boys, and from that point on, a close-knit bond was formed between them all and Bobby. Of course, Ash died alongside the Roadhouse in season 2, but the mother and daughter duo lived to season 5 before sacrificing themselves for Sam and Dean.
Jack Kline
The spawn of Satan, Jack Kline became the fourth member of Team Free Will upon his debut in season 12.
Jack has quite the journey in his three seasons on the show, from finding his way in the world to forming a bond with Dean, Sam, and Cas, all the way to taking away God's power and becoming God himself. Jack was a great character whom not everyone was on board with, but who was crucial to the Winchester story, especially with his reconstruction of heaven.
Rowena MacLeod
A couple of villains in Supernatural begin as just solely intent on doing bad and being enemies of the Winchesters. However, there are those who grow and have an arc that leads them to be close friends and allies to the brothers, one of which being Rowena MacLeod.
Perhaps the most powerful witch on the planet later turned Queen of Hell, Rowena debuted in season 10. She, like many, dies a couple of times, with her final time being an emotional one for Sam and Dean as she sacrifices herself to put all the souls of hell back where they belong. She was sassy, hilarious, powerful, and a badass consistently for five seasons of the show.
Lucifer
The entire Kripke-era of Supernatural was building up to Lucifer being the final big bad that Sam and Dean take on. While the first five seasons did not disappoint in that regard, Lucifer remained a pretty great part of the show way beyond that.
Debuting in the final seconds of season 4 before taking over his vessel in season 5, Lucifer was a fantastic villain throughout Supernatural, all the way up to season 15, where he met his final and decisive end at the hands of Michael. Sarcastic, evil, powerful, and despite some extremely low points, the show often found ways to keep Lucifer a great, entertaining character.
Crowley
Going back to the idea of villains who turned into heroes, Crowley was the original version of this before his mother burst on the scene, and for seven seasons of Supernatural, the King of the Crossroads turned King of Hell was one of the best characters on the show.
A manipulative mastermind, an evil demon, a resourceful ally, a sassy friend, Crowley fulfilled every role he could as a foil for Sam and Dean from the moment he debuted as a sleazy crossroads demon in season 5. Crowley's final sacrifice in season 12 to save the brothers was emotional and a great end to his arc, even though he really should have appeared at least once more after that went down.
Castiel
There is absolutely no debating the fact that Castiel is the most important Supernatural character to be introduced after the first season of the show, becoming the third main character from the moment he debuted all the way to the show's end.
Castiel made his entrance in an epic manner as the one who gripped Dean tight and rose him from perdition. It was the start of a beautiful friendship/fan-ship. Castiel struggles with humanity and morals throughout the show, but he still, he remained adored by fans and is arguably Supernatural's best character not named Sam or Dean.