With Supernatural, along with similar programs such as Buffy the Vampire Slayer.
While Supernatural is arguably the most popular program to come out of the CW, the series owes some of its success to Buffy the Vampire Slayer. Many of the latter show's stars made guest appearances on Supernatural, Buffy patented the mix of fantastical action and character-driven drama that Supernatural became famous for. Both shows put a great deal of focus on family, a fact that explains why the characters between each property are quite similar.
Lucifer And The Master
In of motivation, Lucifer and the Master are eerily similar. Both are trapped in Hell and long to escape in order to eradicate humanity and exact revenge on the people who locked them up.
Beyond their goals, Lucifer and the Master also share important personality traits that lend to their memorability. They both are snarky, charismatic villains who happen to have an explosive anger and a surprising fixation on family. The Master might be more calculating and hammy than Lucifer, but it's clear that the two are cut from a similar cloth.
Crowley And Spike
As esteemed, soulless beings who sport British accents, Crowley and Spike became fan-favorite characters for their respective shows. A lot of it has to do with each actor’s natural charm, which helped sell the sharp and snarky dialogue they spat out in so many scenes.
Beyond the superficial aspects of Spike and Crowley, the two characters went through similar emotional arcs. They started out as genuine threats to their show’s protagonists before becoming reluctant allies who attempted to hide their iration for their former enemy.
Jody And Joyce
Joyce Summers was a Buffy than Jody Mills was on Supernatural, but this fact does little to diminish the similar roles the characters shared. They both started as naive to the dangers of the supernatural before being brought into the fold and becoming a confidant for each show's protagonist(s).
The most important similarity between Jody and Joyce has to do with their relationship with the other characters. Both acted as mother figures for their respective shows, with Joyce obviously being Buffy's mother while Jody acted as a surrogate for Sam and Dean (prior to the return of their actual mother).
Garth And Wesley
While Garth shares much in common with the Buffy character Oz - both are werewolves who help fight monsters before isolating themselves to keep their friends safe - the character's role on Supernatural better matches that of Wesley than Oz.
Both characters start out as allies for the protagonists, where they're introduced as a replacement for the mentor figure. In their adventure, they initially appear to be incompetent at fighting monsters before proving their skills and cementing themselves as reliable. For Garth, this leads to him taking on Bobby's role after his death while Wesley doesn't flourish until he is brought to LA and made a regular on Angel.
Charlie And Willow
It doesn't take a genius to draw the connections between these two characters. Both are nerdy redheads who happen to be tech wizards (Willow in a more literal sense given she's a witch), a surrogate sister for their respective families, and positive LGBTQ+ role models.
In addition to the role both characters play, Charlie and Willow also share similar personality traits. The two often put the needs of their friends above their own, are rather timid around others (though willing to assert themselves in the company of their friends), and are some of the most comionate characters in their respective series.
Jack And Dawn
Though Dawn is considered to be a far more annoying protagonist than Jack, the two characters share much in common. They were both introduced as plot devices to motivate the characters, and took on the stock role of “the youngster.”
Being introduced late in each show’s run meant that Jack and Dawn were often standing in the shadow of their idol. It resulted in tension and occasional arguments with more popular characters, yet the drama was usually a result of their attempts to escape the overbearing control of Buffy and the Winchester brothers, respectively.
Castiel And Angel
While Castiel is much more of a fish out of water than Angel, the two characters embody similar archetypes. They’re brooding loners who wear trench coats and happen to be in love with each show’s main character (a fact that is mostly kept under wraps on Supernatural).
The most significant similarity between Castiel and Angel stems from their character arc. Both were introduced as enigmatic beings who were just as much an asset to the protagonists' crusade against the supernatural forces as they were a potential threat before falling prey to darkness and being sacrificed in an attempt to save the world. Castiel has ittedly died more times than Angel, but the comparison is still apt.
Dean And Faith
Despite a popular meme that posits that Dean would be best friends with Buffy, the monster hunter has far more in common with Buffy's other Slayer. They both are impulsive, sexually promiscuous, and far more laid-back than their hunting partner.
Perhaps the most striking similarity between the two characters is their struggle with anger and jealousy. While Dean never turned to the dark side as Faith did, he felt neglected by his father similarly that Faith believed she was ignored by the Scooby Gang, thus explaining both characters' tendency to lash out at others.
Sam And Buffy
While it would be easy to match the characters together because they're both pretty and receive top billing on their respective shows, that would undersell the surprising nuances Sam and Buffy share. Both are graced with supernatural powers that they didn't ask for and both initially reject the call to adventure in an effort to lead ordinary lives.
Sam and Buffy share more than just a familiar origin story. The two characters frequently butt heads with their "family," they both are among the bravest characters on Supernatural and Buffy, and, most importantly, have both sacrificed their lives to save the world (before being brought back against their will).
Bobby & Giles
On the surface, Bobby and Giles seem like polar opposites. The former is a gruff hunter who frequently gets his hands dirty while the latter comes across as a stuffy bookworm who has never spent a day doing hard labor.
While these aspects serve as a stark reminder of how different each character’s background is, the two both inhabit the mentor role in their show. They’re well versed on supernatural matters and also act as parental figures for the protagonists.