Paul Wesley and Joseph Morgan are all set to wow fans in Star Trek: Strange New Worlds, and DC's Titans, respectively. In The Vampire Diaries, their characters, Stefan and Klaus, shared a unique love-hate relationship, and even though their friendship was confusing, they were very similar to each other.
Stefan thought he was better than Klaus, but the Original saw something of himself in the younger vampire, which was why they bonded. Even though Stefan tried to be better, season 3 saw him get drawn to a darker path - to the point where he even began to espouse a lot of Klaus' ruthless thoughts, mannerisms, and beliefs (which terrified the residents of Mystic Falls).
“The Pleasure I'll Get Of Watching You Suffer Is Greater Than Any Pain I'll Ever Feel.”
Stefan To Katherine In Season 2, Episode 11 "By The Light Of The Moon"
One big similarity between Stefan and Klaus was their hatred for Katherine, albeit for different reasons. Katherine had hoodwinked and turned Stefan into a vampire, and she had annoyed Klaus by delaying his wolf ritual.
Given that she schemed and tried to ruin their lives, it's not surprising that Stefan's hatred for the 500-year-vampire ran as deep as Klaus' (as emphasized by this quote). Not only had she stalked him, but she also manipulated and hurt his loved ones because they got in the way of her desires. The only difference between Klaus and Stefan is that the younger Salvatore brother succeeded in killing the Petrova doppelgänger
“To Beat The Villain, Damon. You Have To Be The Better Villain.”
Stefan To Damon In Season 3, Episode 11, "Our Town"
Otherwise benign, Stefan knew exactly how to play the villain game — it required being worse than the evil they faced, and Stefan wasn't afraid to do that.
Klaus was known to be the most wicked of all villains on the show, and he never hesitated to manipulate, lie, hurt, kill, or otherwise hurt his enemies, so long as he got what he wanted. While he was known to be the kinder Salvatore brother, Stefan's did get caught up in this darker cycle, and was seen to be acting a lot colder and distant towards those he loved. He may have thought keeping them at a distance would protect them in the long run, but damaging these relationships ended up having huge consequences in the future.
“I Know You Were Daggered For A Little While... But Knocking Is Still A Thing.”
Stefan To Rebekah In Season 4, Episode 11, "Catch Me If You Can"
Making jokes about Rebekah's daggered state was a trait that Stefan and Klaus shared, the only exception being that Klaus did the daggering, and Stefan only taunted her without doing the deed.
Like Klaus, Stefan knew where to aim at Rebekah to make it hurt, and her repeated daggering was one of her weak points. Looking for vulnerabilities and using them to one's advantage was a shared quality, and it made TVD fans agree with the iconic Rebekah even more as she was taunted by them.
“Silas Needs To Die. And I Need To Be The One To Kill Him. End Of Story.”
Stefan To Elena In Season 5, Episode 7, "Death and The Maiden"
A thirst for vengeance burned in Stefan after he felt wronged, and his holding a grudge against his oppressors was reminiscent of Klaus. Klaus, too, never let a chance for revenge him, and chased his victims to the edges of the Earth.
Stefan had two such moments, once against Silas (as evidenced by the quote) and once against Klaus himself. When he had decided that he wanted to end someone, he only saw red.
“You're My Brother. I'm Not Gonna Give Up On You. I Never Will.”
Stefan To Damon In Season 5, Episode 14, "No Exit"
Stefan and Damon's brotherly moments on The Vampire Diaries are legendary, and their relationship is often compared to Klaus and Elijah's. Both Klaus and Stefan cared deeply for their brothers, and they would give up anything to save them.
They both knew how much they owed their brothers, and how nobody was closer to them than their family. They even risked their own lives for their older siblings because they couldn't bare to be without them or see them in pain. Given that Stefan and Damon found peace together, and Klaus and Elijah died in each other's arms, fans can clearly see they had an unbreakable bond.
“Come On, Damon. You Think I'm Afraid Of A Ripper? I Invented The Word.”
Stefan To Damon In Season 5, Episode 14, "No Exit"
Having been at their absolute worse in their anger and humanity-less times, Stefan and Klaus were unafraid of taking on lethal creatures because they had been there themselves.
With his Ripper sprees, Stefan knew how the minds of these vampires worked and how to outsmart them, just like Klaus knew how to take on the worst nemesis because he was pretty brutal himself. If Klaus didn't end up heading off to New Orleans to start afresh, fans would have loved to have seen the two of them team up a lot more.
“You Are An Embarrassment To Humanity-Free Vampires Everywhere.”
Stefan To Caroline In Season 6, Episode 17, "A Bird In A Gilded Cage"
With his humanity switch flipped, Stefan liked to enjoy the violent aspects of vampirism, much like his Original sire Klaus. This was why he let Caroline know that her turn without humanity was not nearly as vicious as it should be.
Violence was a part of Klaus' DNA, too, and he truly believed that, as the superior species, vampries should kill rampantly to really get the vampire experience.
“I Understand If I Have To Wait For You. And I Will. I'll Wait. And When You're Ready For Me, I Will Be Ready For You.”
Stefan To Caroline In Season 6, Episode 22, "I'm Thinking Of You All The While"
A big common factor between the two was their love for Caroline. Many TVD fans would say Klaus and Caroline were soulmates, but she eventually chose Stefan to wed. Both the vampires had chosen to wait for Caroline to be ready for them.
Klaus offered her the world, and told her that he would be around if she ever chose to change her mind. Similarly, Stefan gave her time and space as they healed their friendship, so that they could be together.
“My Mother Was Practically Ripped Out Of My Arms [...] You Don't Move On From That. You Find Distractions.”
Stefan To Lily In Season 7, Episode 3, "Age Of Innocence"
Tragic pasts were common in The Vampire Diaries, and Stefan and Klaus both had major parental issues. Their unhealed trauma from abusive fathers, and mothers, who wanted the best for them but could never quite achieve that, left them with love-deficient childhoods.
Their issues continued into their adult lives, and Stefan found ways to mask his feelings of inadequacy and loneliness, akin to Klaus.
“No, I'm Choosing Myself Over Everyone Else.”
Stefan To Cade In Season 8, Episode 9, "The Simple Intimacy Of The Near Touch"
It was rarely in Stefan's nature to put himself first, but in this instance, he did exactly what Klaus would do — look out for his own interests. Klaus rarely cared for anyone but himself, and made sure that everyone knew of his calculative nature.
Working for Cade was what Stefan thought he deserved, even if that was not true. He had no humanity and wanted to be left to his own devices, choosing his own abandon over everyone else.