Type of Villain
Elijah Mikaelson is the deuteragonist villain of The Originals as well as the third oldest of the Original Vampires (particularly the siblings) he is the younger brother of Freya and Finn, the older brother Kol, Rebekah and older half-brother of Niklaus, as well as the youngest son of Mikael and Esther.
Lucien Castle was a major recurring character and the main antagonist in the third season of The Originals. He was an Upgraded Original Vampire, the first and former vampire turned by Klaus Mikaelson as well as the first vampire to be turned overall, and a member of the Trinity.
Klaus Mikaelson is the strongest of the Originals. His powers are more advanced and potent than that of his Original siblings, including his step-father, because of his Werewolf side.
Although his brother Klaus might technically be stronger — Klaus is half vampire, half werewolf — Elijah is the most powerful. Other traits to note: He is level-headed.
Other than Klaus Mikaelson, Marcel Gerard is the longest-tenured, strongest, and most terrifying villain in The Originals. He continues to antagonize the main characters throughout five seasons, using dastardly ruses and devious ploys to keep his odious agenda secret.
For pretty much all of Klaus' vampire life, Mikael was the only man who was physically capable of fighting Klaus, who actually had the drive and determination to kill him, and most importantly had the only weapon that could actually kill Klaus.
Klaus Mikaelson
The nastiest of the Mikaelson bunch, so much so that he warrants his own entry on this list. Klaus (Joseph Morgan), like his family, is an Original vampire, but unlike the others he also has werewolf blood, a unique Original Hybrid.
With all of this in mind, it is important to note that Rebekah is the weakest Original Vampire, I wouldn't necessarily say because she's female, but for the sake of this argument, it's worth noting this, but at the end of the day she might have simply been the weakest child of Esther (strength-wise), and not because ...
However, it is Lucien Castle's serum the flips the balance of power between Klaus - the most powerful Original due to his combined vampire and werewolf bloodlines and diabolical personality - and his long-time frenemy, Marcellus "Marcel" Gerard.
After Tristan de Martel was disposed of, Marcel became the leader of the Strix. With Davina's death in season three, Marcel declared war on the Mikaelsons and became the Beast of prophecy when Elijah killed him.
Before her death, Davina forgives Marcel because he saved her and accepts her fate, because she thinks that it would be selfish to take everyone else with her. Her throat is later slitten by Sophie to complete the Harvest, but she does not come back. She is left to be mourned by who watched it.
Type of Villain
He was introduced as the main antagonist of The Originals due to his diabolical tactics to keep his position of power and has shown to be a major enemy of Klaus as Klaus gave the impression that he would exploit Rebekah.
Physically as of now, Marcel is stronger because of Lucien's werewolf toxin serum. Basically, Marcel is an original vampire who also has werewolf venom in his bite that even Klaus can't heal.
However, with anger or being empowered by a specific date in the astrological cycle, Hope could surpass Marcel in brute strength.
Powers and Abilities
As the Original Hybrid, Klaus is the strongest of the Original vampires due to his Werewolf heritage giving him additional powers and advantages his half-siblings do not possess, making him the most physically powerful immortal being in the world, second only to Marcel Gerard.
From his strength to senses to healing powers and even telepathic abilities, Klaus was more superior to his siblings since he had both vampire and werewolf genes in him.
By feats Bonnie simply outclasses Hope by a huge margin. Even by character hype, while Hope was said to be able to fuel the NO ancestors for generations, Bonnie was said to be able to do anything she put her mind to.
Klaus: Because He's The Ultimate Mastermind
Klaus is the most terrifying Original because he is so much more than an Original. He's also a hybrid, and he's also a man who always comes into every situation with a plan.
Kol Mikaelson is known to the world as the wildest Mikaelson, the troublemaker, however to his family he's the burden, the last priority.
Kai never had any friends, being a sociopath and nobody ever thought of him in a nice way, not even his family so he had no one to give him a chance. Basically, I think Klaus was the worse villain who became a better man but Kai is just a bad villain who never had a chance.
BEST: Marcel Gerard
Though Klaus sees him as a son, his jealousy gets the best of him and forces Marcel to become an enemy. Without the love that exists between the two vampires, there couldn't be such a rich animosity. His ability to conspire against Klaus makes him a smart foe.
Esther is, along with Mikael, one of the two beings that Klaus truly feared; Klaus is only afraid of Esther, because she knows the Spell that turned him and his half-siblings into vampires, or in Klaus' case into a hybrid, and can turn them back into humans again, or in Klaus' case into a werewolf again; however, ...
He mentioned in season 1 of the originals that his kill count is in hundreds of thousands I think a minimum of 352,000.