The Originals focuses on the first family of virtually indestructible vampires, but Marcel Gerard is the strongest vampire on the series. A spin-off of The Vampire Diaries, The Originals features the first family of vampires, the Mikaelsons. The show is set in New Orleans and follows the Mikaelsons, particularly Klaus, Elijah, and Rebekah, as they deal with family drama and threats from supernatural foes. The show also explores the personal relationships the siblings forged with friends, lovers, and enemies throughout their 1,000-year existence. One reason for the Originals' longevity is that they are impervious to the threats that kill other vampires such as Stefan and Damon Salvatore.
On The Vampire Diaries, the Originals can walk in the sunlight without daylight rings, compel other vampires, and are only temporarily deterred by a wooden stake to the heart. The weapons effective against the Mikaelsons are a silver dagger dipped in White Oak ash (The exception is Klaus whose werewolf side enables him to heal from the silver.) However, if the blade embedded in the heart of a Mikaelson is removed, they recover and resume their powers. A stake forged from White Oak is one of two ways to put down a Mikaelson vampire for good. The White Oak tree, one of nature's eternal objects, was the ingredient in Esther's spell that made her children immortal, but it can take that immortality away. Witches who possess a large amount of mystical energy are formidable foes. Because every vampire's origin can be traced back to the Mikaelson siblings, if one dies, so does their sire line. This affords them a great deal of protection when battling their enemies.
On The Originals, the Mikaelsons face threats that expose new weaknesses. Papa Tunde's blade made from the skeletal remains of the Hollow is a dark object that renders an Original unconscious and inflicts upon them agonizing pain. Davina and Kol create a gold White Ash dagger that has the same effect on Klaus that the silver dagger does on his siblings. 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. During season 3, which aired at the same time as The Vampire Diaries season 7, Lucien replicates Esther's vampirism spell but adds the venom of the seven werewolf bloodlines. Marcel drinks the serum and becomes an "enhanced vampire" able to kill an Original with one bite. He emerges as the show's most powerful vampire and the biggest threat to Mikaelsons' survival. Marcel is also able to compel an Original -- the only supernatural creature who can control their minds.
Freya develops an antidote during season 4, but the scales are still tipped in Marcel's favor. Marcel's blood mixed with the Hollow's magic is a deadly combination as well. As long as Marcel lives, Klaus' power pales in comparison. Klaus' paranoia, ambition, rage, resentments, and betrayals lead to his downfall. His determination to uphold his family's oath of "always and forever" means destroying others to achieve his goal. When he sacrifices Davina's life to save himself and his family from Lucien, he breaks a promise to Marcel, who has always felt like an outsider. To exact revenge, Marcel drinks the serum and rallies Klaus' enemies, which only serves to reinforce his control over Klaus.
Once Davina breaks Klaus' sire line during season 3, she frees Damon, Stefan, and Caroline Forbes from his grip. The connection thwarted Their previous plan to kill him. Klaus becomes vulnerable since those he sired can kill him without repercussions. Klaus' past misdeeds have also put his daughter Hope in danger, and these threats could come to pass on Legacies. During season 5, Klaus is ultimately defeated by the spirit of the Hollow, forcing him to end his life or risk destroying everyone he loves. Had he lived, fueled by an evil spirit, he would have been unstoppable. By the series finale of The Originals, his lust for power, much like the power he previously enjoyed, fades.