Bill Forbes is Caroline's dad and, although he detests vampires with every fiber of his being, he is one of the most mentally powerful humans in the entire series. Unlike most humans, Bill cannot be compelled because he trained himself to resist compulsion from even the most powerful vampires.
In A View to a Kill, Kol was killed by Jeremy and Elena. His compulsion over Damon has been lifted after his demise.
In the season one finale, Caroline is severely injured in a car wreck and suffers from internal bleeding. Damon Salvatore feeds Caroline his blood to heal her. Later that night, Caroline is smothered to death with a pillow by Katherine Pierce, who found out that Damon gave her some of his blood.
In Bringing Out The Dead, Bill was killed by Alaric Saltzman (while Alaric was taken over by "The Darkness"), who stabbed him to death and cut his throat while having vampire blood in his system. He woke up in transition but chose not to feed and turn into a vampire.
Any supernatural beings cannot be compelled by any other supernatural beings with some exceptions. Only Original Vampires can compel other vampires.
Damon's ability to drink human blood gives him more vital senses of strength, speed, compulsion, and other vampire tricks that do not work as well for Stefan due to the lack of human blood he consumes. Stefan admits that he is not as strong as Damon and thus would not be able to win in a fight.
Silas is the world's first immortal who's also the most powerful vampire in the TVD universe, although his powers have only been used as plot holes.
Alaric Saltzman
Alaric, who has had his fair share of funny scenes, is certainly one of the most powerful humans on The Vampire Diaries. He also dies several times and even becomes an Original vampire for a while, but, as a human, he is one of the most resourceful, protective and trustworthy allies anyone can have.
Yes so Alaric travelled over the line and his vampirism was removed by the purification spell - he was resorted back to the state he was in at his last point of being human: dying.
Hope Andrea Rebekah Mikaelson is a vampire-werewolf-witch mortal tribrid. She is the daughter of Niklaus Mikaelson and Hayley Marshall-Kenner.
* Why is Elena feeding on Damon's blood such a big deal? "That's a little bit of a shout-out to the books, but also just to vampire folklore in general. If you look at any of it metaphorically, it's a very intimate exchange of bodily fluids. So you can read into that what you will," she says.
Damon apologizes for everything bad he's done to her and she forgives him, lying down next to him. He then tells her that he loves her as tears roll down her cheeks. Damon says she would have liked him in 1864, and Elena tells him that she likes him now.
Julie Plec confirmed that Klaus is the origin of the bloodline Stefan, Damon, Caroline and Elena are from. It is possible to unlink a vampire from their bloodline using magic. This was successfully performed on Klaus by Davina. For reasons unknown, Klaus never sired new vampires after his sireline was severed.
Alongside Damon, Elena got everything she had wished for since becoming a vampire. As well as rendering her human, the cure also had a bonus side effect. Similar to when a human becomes a vampire, the transition serves to break any and all past compulsions.
In season two, Damon is forced to compel Elena to forget that he ever loved her. This was one of the most heartbreaking scenes in the series, and it showed how deeply their connection ran. Damon was willing to give up his happiness to protect Elena, an act that demonstrated their intense bond.
Original vampires can compel both humans and non-Original vampires, but not their fellow Original vampires (as Rebekah pointed out to Kol). When an Original vampire dies, their compulsion wears off.
In Do Not Go Gentle, Esther modified her original spell and turned Alaric into an Enhanced Original vampire. The spell, however, had one major addition. Since Esther's spell called for the need of the doppelgänger's blood to cast the Immortality Spell, she took the opportunity to bind Alaric's life to Elena's.
Through overuse of the Gilbert Ring, Esther manipulated his spirit while he was on the Other Side before he would resurrect, and as a result he developed an alter ego, called The Darkness by Bonnie and Dark Alaric or Evil Alaric to others, that hated vampires and vampire sympathizers; as the Darkness, Alaric killed ...
Throughout The Vampire Diaries Series
In Do Not Go Gentle, Esther Mikaelson possesses Bonnie's body to feed Alaric her blood as he is about to die in transition from dying with vampire blood in his system. He is then turned into The Darkness as a vampire, unable to grasp sanity, until he is killed when Elena drowns.
The story of Sekhmet, the Egyptian feline warrior goddess associated with both plague and healing, is considered by some to be one of the oldest vampire tales. Legend holds that the sun god, Ra, sent his daughter Sekhmet down to punish humankind for their disobedience.
The age difference between the two is too minor to make much of a difference. The more decisive element is that Elena has had some combat training from Alaric and Damon. Caroline is actually Stronger, but Elena was trained to kill vampires as a human.
Like all vampires, Elena has the average abilities such as super speed, immortality, super strength, instant healing, heightened senses, compulsion, etc. But, due to the fact that she has only just completed the transition, she is still fairly weak in each and every ability she has.
She can take on Stefan and Damon easily without even breaking her finger. The only thing that would stop her killing anyone that gets in her way is so she doesn't wear down her heels! Definitely should be above Damon. She is by far the strongest non original.
It's only partially because of experience. In most vampire stories, the "disease" progresses and makes them stronger over the centuries. Abilities manifest at certain times; i.e., the ability to fly, start fires remotely, etc. Their strength also increases the longer they live.