The Vampire Diaries successfully ran for 8 seasons and featured epic storylines. While we have met many friends and enemies through its duration, the main characters pretty much stayed the same, excepting Enzo who went from side character to series regular in the last couple seasons.
However, out of our group of main characters, how do they rank concerning their intelligence? Read on to find out more.
Jeremy
Jeremy always seemed a step behind others. He is younger than the other main characters, and Elena does try to shield him from harm. However, it could be that this shielding didn't help out much in sharpening his intellect. For many of the seasons, others protect Jeremy. Later, he does come into his own, and if he has more of a role in the spin-off Legacies we may see a change in his intellect.
Tyler
Tyler became a much more intriguing character when he turned into a werewolf. However, he easily accepts being a hybrid to Klaus at first without realizing Klaus's other intentions. Tyler is happy not to have to go through the pain of turning and to have more power, but being sired to Klaus as a hybrid means that he has to follow Klaus's every order. Later, this is changed, but initially, this is the way it was.
Later, Tyler becomes obsessed with a revenge plot. Not too smart, he cares more about this than Caroline, and he doesn't work with any of his friends. A lone wolf, he doesn't realize that his friends and he are much more successful when they do things in a pack.
Matt
Matt is the steady friend, and the only one steadily human throughout. In some ways, his distrust of the supernatural (especially the Salvatore brothers) does make him a little smart. He understands that they are dangerous and much more of a threat than his friends imagine. However, Matt doesn't often see the shades of the gray in the situation. This was apparent in how he seemed to despise Caroline when she first became a vampire. Additionally, he quickly follows anything that Elena asks of him, which could mean that he is loyal (which he is) and also that he isn't always as bright as the others.
Damon
Damon can be intelligent, when it suits him and his situation. He does understand that drinking human blood, rather than vampire blood, gives him more power. Also, he is willing to be the villain if that means getting the job done. In a later season, he used this idea of him as the villain to his advantage. True villain, Kai, had linked Bonnie and Elena's lives. When Bonnie was alive, Elena would be in a sleepy beauty-like spell. Once Bonnie died, Elena would awaken. So Kai presented Damon with a nearly impossible decision: save Bonnie or let her die so that Elena can come back to life.
Damon acted as if he was going to let Bonnie die, but he used that moment to walk away and then behind Kai to kill him. Then Damon ran to save Bonnie. The one thing that holds him back is that he blames all his bad behavior on others. For an older brother and a 100-year-old vampire, you'd think he'd be smarter than that.
Stefan
Stefan does seem a little brighter than his brother, at times. An example of this is when he outwitted Klaus. He was able to see the one weakness that Klaus had was Klaus's family. Although Klaus put a stake in his family members, putting them in a decomposed sleep state, he cared about them and made sure that their coffins were with him.
By taking the coffins, Stefan understands that the group can have a little power over Klaus (a little being the important word). Other times, Stefan gets caught up in his Ripper tendencies, his hero hair, and his almost teenage-dramatic emotions. Maybe since he was killed when he was a teen, his teen dramatic self stayed intact.
Enzo
Initially seen as an old friend that is a bad influence on Damon, Enzo develops. While he wasn't too bright when he was with Damon's mother, his intelligence came out more with the siren. Even under the siren's control, he gives Bonnie hints about what's happening.
The siren was doing brain control on Damon and him in order to get them to commit heinous acts. While Damon gives up, Enzo tricks the siren. He finds a way to hold on to his humanity and his love for Bonnie. He tells Bonnie, "I will never stop fighting. I will brave the oceans and sail past the sirens to find my way back to you." Later, he does get taken over by the siren, but Bonnie gets him to come back, and honestly, he comes back faster than Damon did.
Elena
Elena's main intelligence is in bringing people together. Her fierce compassion and loyalty give her an emotional intelligence unparalleled on the show. Due to this, she seems to know the good that characters are capable of without them even knowing it. She figures out how to help Stefan get out of his dangerous Ripper stage. In addition, she has moments of intelligence--like giving Katherine the cure or in tricking Rebekah.
But, her self-righteousness, her doing the perceived "right" thing behind others' back takes her intelligence down a notch. However, we recognize that Elena has stayed alive not just due to being a damsel-in-distress but because she creates community. This is Elena's super power and intelligence.
Alaric
Alaric has gone through many changes during his time on The Vampire Diaries. He's had to adjust his worldview many times, but through it all, he learns. Alaric is a successful teacher because he is a successful student. He's willing to learn and share his knowledge. In addition, the others count on Alaric almost as if Alaric were a library of knowledge, and he is that.
Caroline
Once she becomes a vampire, everything that is good about Caroline intensifies. She is incredibly type A, but she is also even more kind and intelligent. When "Tyler" rescues her and they begin to make-up in the woods, she quickly realizes that it is Klaus in Tyler's body. When the Heretics had poisoned her skin, making it vervain, she and Stefan figure out how to get the Heretics to reverse the spell.
Caroline is clever and bright. She is as Klaus said, "such much more than a pretty face."
Bonnie
Bonnie is the one that Elena and the others often depend upon to save them or to improve the situation. She figures out how to get Damon out of the Gemini hell-world, and luckily, Damon doesn't give up in helping get her out either. She also brilliantly figures out how to trap Kai in a new hell-world, built by Caroline and Alaric's young Gemini twin daughters.
While she does seem to be taken advantage of by others, there is no doubt that Bonnie is smart and becomes even smarter through the duration of the series.
Katherine
Katherine survives being chased by Klaus for 500 years. While human, she realizes that Klaus is trying to sacrifice her, and she wants to live. The only way that she can live and be of no use to Klaus is to become a vampire. She finds a way to do this. As a vampire, her intelligence intensifies.
Trying to make herself stronger, she even finds a way to develop a tolerance to vervain. She builds strength, and even when she seems kicked low to the ground, she finds a way to bring herself up. Make her die a human death, she finds a way to jump into Elena, surviving in another's body. Drag her to hell, she finds a way to become the queen.