Big Bad

A Big Bad is the term applied to the greatest adversary of each season.

The Originals: Prodigal Son

 * The Hollow: An ancient demonic force that seeks a corporeal vessel in the material realm. For thousands of years it has plagued Gabriel's maternal bloodline, having been originally conjured by Qetsiyah, the spurned lover of it's oldest known ancestor, Silas. It eventually finds a host in the teenaged Tribrid, but he is eventually able to banish it from his body as it takes on the form of deformed and corrupted doppelgangers of both the teenager and it's previous hosts, Silas, and Inadu, whose souls it can command. He manages to destroy it's earthly tether before it is then sucked into Klaus, who kills himself to destroy the Hollow forever.

Legacies: Season 1

 * Malivore: Malivore is a sentient hell dimension created by an ancient alliance of witches, werewolves, and vampires, to imprison the Dragonborn and many other renegade supernaturals. It's only remaining portal on earth is watched closely by Triad Industries, a powerful corporation that is the modern-day incarnation of the original supernatural alliance that created Malivore in the first place, but the organization and it's owners are unaware that both they and Malivore itself is being manipulated by an external power who seeks control over the forces within. Malivore's master is later revealed to be the demonic Elder God known as Chthon. It is destroyed when Gabriel Mikaelson willingly throws himself into it's black depths for a second time in order to escape from a prison world where it's manifestation was incarcerated, setting off a chain reaction that destroys Malivore but allows many of it's monsters to escape and also erasing everyone's memories of him yet again.

Others

 * Adrienne: An old and powerful vampiress who comes into conflict with Gabriel and his friends.
 * Sybil: An ancient and extremely powerful Siren who Gabriel met as a little boy.
 * Ethan Crane: A handsome vampire who leads a secret cult known as the Vitale Society who tries to use the boy's blood in an attempt to resurrect Klaus by becoming the Original's vessel and taking his power. He is later killed by Gabriel.
 * Cain: The Original Werewolf and one of Gabriel's oldest paternal ancestors.
 * The Phoenix: Gabriel's "evil split personality" who is more of a manifestation of his darkest impulses and instincts.
 * Urizen: An ancient demon god who is worshipped by an extradimensional culture of magi known as the Lescanzi.
 * Blodreina: Josie Saltzman as an extremely powerful and ruthless Vengeance Demon and bloodthirsty conqueror.
 * Emotionless Gabriel: Gabriel turns off his humanity after his girlfriend's death sends him over the edge.
 * Selene Gallio: Gabriel's paternal grandaunt, a powerful witch and the youngest sister of Esther and Dahlia.